Last night on Late Night, Jerry Seinfeld made an appearance on Abbott and Costello's classic "Who's On First?" routine with Billy Crystal and Jimmy Fallon only to clear up the identities of Who, What, and I Don't Know. Plus: Paul Rudd distorted his "Sexiest Man Alive" look; Judd Apatow filled in for Leslie Mann because she had a yeast infection. "The cranberry juice isn't working," he told Chelsea Handler. But seriously, no subject is too venereal nor flatulent for these love birds. And oh, the birthday debauchery Katie Holmes gets into on her birthday — she rides a cupcake sugar high that compels her to get to the set of Dead Accounts on time. Watch our compilation to see what you missed.