According to Chameleon, despite the fact that he is an un-person, he wants to leave an impact on the lives of those he impersonates. Therefore, he deliberately goes out of his way to do things he believes his 'face' would have wanted, but were too timid to. Torment an old tormenter, spite a girlfriend who ditched him, sleep with a woman who's attracted to him, and he's about to do worse. The bit about starting a new relationship while dumping on MJ is good sense from an impersonator's view. Old girlfriend might see through the disguise, new girlfriend won't.