Why did Andy and Keisha break up at the talent show?

Andy's trying hard to put a brave face on his intense emotional pain. At the school talent contest, he's the life and soul of the party, cracking jokes and seemingly enjoying himself. Much to the horror of Keisha, he even starts taking his clothes off on stage. Everyone seems to find this impromptu strip-show hilarious. All except Keisha, that is. (Oh, and the teachers too. But then teachers tend not to find their students stripping off at school to be the height of hilarity).
Nevertheless, the last thing Keisha wants to do is to put Andy on a downer, so she tries to complement him on his unusual performance. But Andy snaps back and belittles her, telling Keisha in no uncertain terms how much she gets on his nerves. The two get into a fight, which ends with Keisha angrily storming off before she gets a chance to perform her song.