1: The act of being irrationally, illogically completly head over heels attracted and in love with the Tokio Hotel lead singer Bill Kaulitz.
2: the act of being sexually aroused by the voice, presence, or thought of the Tokio Hotel lead singer Bill Kaulitz.
I've actually done that to a few of my friends before. I'd pull up a picture of him, and ask:
"What d'ya think? Hot or not?" and they'd all gleefully exclaim stuff like 'hell yeah' or 'I'd do her' or 'damn she's fine' and I just burst out laughing and tell them that she is actually a he. Then I'd have to prove to them I was telling the truth and what not but what really surprises me is that more than a few of them always keep looking at him with that same (now hidden) lust in their eyes. I think all guys are a little billsexual inside.