The pro-McGregor crowd at Dublin's Convention Centre went wild as the challenger reached over and grabbed Aldo's belt as the two traded barbs during the latest stop of their promotion tour.
UFC president Dana White failed to head off McGregor as he went for the shiny belt. The UFC boss then had to keep the two fighters apart until the belt was retrieved from McGregor and returned to Aldo.
The two fighter traded insults the entire time until peace was restored.
White had to hold the two fighters apart again later when they met centre stage for the latest in a line of tense staredowns, both men jawing at each other.
The two fight for real July 11 at UFC 189 in Las Vegas.
The UFC 189 World Championship Tour, which kicked off March 20, also took the fighters to Rio de Janeiro, Las Vegas, Los Angeles, Boston, New York and Toronto.
The two almost came to blows in Toronto when McGregor slapped Aldo's back during a break in a TV appearance on "Canada AM."