The guy who takes one for the team. He's the guy who goes with the ugly/large/psychotic (delete as appropriate!) woman of the pack, so his mates can get off with their better looking mates. The move is usually an aggressive, bold action, so as to get it over and done with...
Spike: 'Look at Oggi necking the fat chick!'
Frank: 'Trust Oggi to be the Ice Breaker!'
Spike: 'We're quids in! Jingle bells, jingle bells, shagging all the way!!'