It's not that he wouldn't sleep with her under the right circumstances, but that, perhaps, the right circumstances haven't presented themselves. Prom room of weirdness and headaches notwithstanding.

He has never claimed to not be evil.

Those three little words - no matter how fast she spits them - make him grin like a Cheshire cat. It widens when she mentions 'creepy', because, "You're not creeped out. You are the polar opposite of creeped out by me."