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.
Anyone that finds themself attracted to the notoriously androgynous Bill Kaulitz regardless of their previous sexual orientation.
"What's with that Bushido guy always flirting with Bill? Is he gay or what"
"No man, he's Billsexual"