(Rachel, looking to see Chandler's "thing", saw Joey in the shower instead)
Phoebe: (to Joey, entering Monica's apartment) Hey, Joey. What's going on?
Joey: Clear the tracks for the boobie payback express. Next stop... Rachel Green!
(He goes into the bathroom, we hear a scream. He comes out, closely followed by Monica in a towel)
Monica: Joey!! What the hell were you doing?!
Joey: Sorry--wrong boobies!