Then, somehow, the in-flight entertainment system threatened to take the discomfort up a notch.
See, Miller had selected "Black Swan," Darren Aronofsky's surreal 2010 drama about hyper-competitive ballet dancers, as her coach-coping viewing strategy.
Miller expected an escapist joy with an Oscar-winning pedigree. She perhaps didn't expect the highly suggestive love scene between stars Natalie Portman and Mila Kunis that was soon flickering inches from her eyes — and, as it turns out, the eyes of her two prying, underage flight neighbours.
She knew it wasn't necessarily appropriate content for the kids next to and behind her. She also didn't really care.
"Oh, that awkward moment where everyone is staring at you because the sex scene is on," Miller said with a boisterous laugh during a recent telephone interview.
"I didn't know what to do. So I just kept watching it. That's what I did."
In fact, the public preponderance of iPads, tablets, laptops and smartphones has led us to a relatively uncharted realm of etiquette — is it socially acceptable to watch R-rated, adult-oriented material on a screen in public, particularly when children are around?
Or, with more people than ever indulging in HBO-on-the-go in crowded coffeeshops, commuter trains and airport lounges, is the onus on those with delicate sensibilities to keep their eyes off others' screens?
Jackie Gamble, a flight attendant with a Canadian airline, says it's not uncommon to see passengers indulging in some risque material while soaring through the sky.
"You see people watching things and you're like: 'Whoa,'" she said, noting however that she'd never seen anyone watching "full-out porn."
"If someone brings it to my attention for example, or if I see something that I deem to be really over-the-top, then I would say something."
A WestJet representative similarly said passengers complaining about adult content on others' screens is "not an issue."
"Our guests understand there are a variety of age groups that travel on our airline and choose content they feel is suitable," wrote Jennifer Sanford in an email.
But most people have faced this issue before, either experiencing screen shame themselves or spying another's screen that features content raunchy enough to raise eyebrows (or ire, as the case may be).
And it seems even parents of young children are flummoxed by this particular question of tabletiquette.
Miller, a mother of three who maintains an award-winning blog about her adventures in parenting at theredneckmommy.com, says it's simply no one else's business what she watches, so long as she's wearing earphones.
"I really don't think it is my responsibility to filter what other people's children are seeing," she said.
"It's hard enough getting through life, being a parent or not being a parent, that you have to worry about small eyes."
Mother of two Julie Harrison — whose Coffee With Julie blog is published at julieharrison.ca — is similarly tolerant of other people's viewing habits, assuming the content isn't extreme.
"If it's on your laptop/iPad and you're listening to headphones ... well, too bad, so sad, for the children's innocence," she wrote in an email.
"Personally, if it was me, I would be too self-conscious and wouldn't even consider watching adult material when children are around. But I can't hold someone else to the same standard."
But other parents disagree, arguing that it's simply common sense not to watch potentially graphic material in a public space.
"I hate to put the onus on everybody to look out for my kids or to meet my standards, but (some) things are so explicit," said Newfoundland-raised mother-of-three Kyran Pittman, whose memoir "Planting Dandelions: Field Notes from a Semi-Domesticated Life" was released in 2011.
"I don't want to be a prude or anything about this kind of thing, but the (newfound) accessibility — with that comes some more responsibility to think about who's in your line of sight for that image."
Pittman, whose family lives in Arkansas, tries to keep her sons away from particularly graphic material. She and her husband wait until the boys have drifted off to sleep before indulging in the aggressively adult fantasy "Game of Thrones," but she notes that "media landmines" lurk everywhere.
Sometimes, her husband drifts off while watching "South Park" on his iPad, and Pittman will stroll through her household hallways and overhear the not-quite-dulcet tones of the show's foul-mouthed elementary schoolers.
"I'm just appalled that any of our kids could walk through and hear what Cartman is ranting about — and they don't get irony," she said.
Arizona-based mother Sheri Wallace remembers a recent flight with her 12-year-old daughter, whose seatmates — older teenage boys — were watching R-rated movies on their in-flight screens. Wallace noticed that her daughter was absorbing the material too.
She didn't say anything at the time, but she thinks it's up to the viewer to be mindful of whether their inappropriate material has found an unintentional audience. And she says a big problem is that most people aren't aware just how visible their ever-brighter, ever-clearer screens really are.
"You become accustomed to the idea that people can't see your screen," said Wallace, editor of roadtripsforfamilies.com. "Five years ago, screens were crappy, and so you couldn't see from the first class seat sitting next to you. But now, you can see all types of information.
"I mean I see a lot of people who are sexting back and forth with their girlfriends — your phone even, is really readable."
And, some parents say, these devices are especially captivating to children.
Toronto dad Jason Graham has sons aged six and 10 who are drawn to bright, colourful screens "like flies to sugar"
"There's no doubt in my mind that if there was ... a tablet or a laptop with a larger screen that was near my kids in a crowded area, their eyes would be drawn to it," said Graham, the only father blogger on urbanmoms.ca.
And if those curious kids ever did find their wandering attention drawn to a scene of graphic bloodshed or sex, Graham says he would be tempted to speak up.
"If there was glaringly questionable content happening and my kid was standing there hovering over (it), I might be inclined to tap that person on the shoulder and say, 'Maybe this is not a good time to be watching that.'"
Indeed, if you try watching "Game of Thrones" — with its artful arcs of spurting blood and long passages of proudly gratuitous "sexposition" — around a parent and his or her young children, it's likely you'll see that breathing fire isn't a skill exclusive to dragons.
But some would argue that eavesdropping on someone else's entertainment is a lapse of manners more severe than watching an adult show on a personal gadget.
"It is so socially unacceptable to look at somebody's screen when they're writing ... and I think it extends to media of any sort on the screen as well," said Miller.
"We're in a new digital age — teach your kid some digital manners.... Teach your kids how not to be peeping toms."
So, which is worse — prying eyes or steaming up the sky?
Daniel Post Senning, great-great-grandson of Emily Post and co-author of the latest edition of "Emily Post's Etiquette," is probably as close to an expert on the subject as there is, having just finished the manuscript for a book entitled "Manners in a Digital World: Living Well Online."
First, he agrees that he would "give someone the benefit of not reading over their shoulder." But he notes that sometimes we are captive audiences for the particular entertainment whims of those around us.
"You're in a line at the grocery store or you're sitting on a plane next to someone or you're in an elevator ... it's not always possible for other people to avert their attention," he said.
"It's not necessarily their responsibility to do so."
Post Senning actually encountered this issue personally on a recent flight, when he queued up 2008's R-rated "The Mysteries of Pittsburgh" on Netflix. Shoulder to shoulder with other passengers in economy, he soon realized there was a "love scene coming fast."
He turned it off immediately. While he wasn't sure whether any children were nearby, he didn't want to risk it.
"One of the fundamental principles or tenets of all good etiquette is consideration of the people around you, having an awareness of how your actions are affecting the people that you're with," he said.
For protective parents, meanwhile, Post Senning has advice on navigating an awkward confrontation with someone viewing salty content in public.
"We often say you don't have standing to correct someone else's behaviour," he said. "But (it's different) if you can approach them in the spirit of, 'You might not know this' — I call it the 'broccoli in the teeth rule.' You approach someone in the spirit of saving them some embarrassment."
As screens multiply in the public eye, clearer notions of etiquette will likely emerge — Post Senning, for instance, points out the popularity of the "NSFW" disclaimer, meant to discourage web surfers from splashing something inappropriate across screens at the office.
Technology could also offer solutions. 3M already offers a "privacy screen protector" for the iPad, a clear adhesive that promises to limit the view of any would-be gawkers approaching a screen from a side angle.
For now, anyway, most people ruminating on both sides of this contentious issue agree on one thing — there's some content no one should watch in public. Ever.
"If you're watching porn in public, that's a problem," laughed Miller. "And that's not the problem of the person staring at your screen over your shoulder.
"You shouldn't be allowed outside the house."