The act of putting a balloon, water balloon size preferably, in another persons anus and then blowing it up with mouth or straw until it pops, causing extensive amounts of pleasure.
James blowbuttaged a handsome chap in the men's room at Bloomingdales...his turgid cock felt good in Jame's mouth and his tight asssqueezing down on Jame's finger made Jame's shot his wad all over the stall floor.