It didn't go so well.
The general consensus following the 'performance' by The Situation was that he bombed, not just bombed but tragically bombed. He was, in fact, booed, heckled and almost cut short of his poorly-delivered spiel. Head roaster Jeff Ross even parachutes in to save him at the end. Too little, too late though.
One important note - about the entire show - is that the 'actor' was chided by almost every member of the roast squad before he came on (a regular roast occurrence) so a return of fire was in order. But Mike's aim was not just misguided, it actually boomeranged back to himself.
The following video will probably be removed because, well, it's illegal. But, that's YouTube's problem. Enjoy while it lasts: