When someone is doing things a crackhead would do, such as: sell things they own for cheap, try to get money, act shady, bother you constantly. Behaving as a crackhead would.
Mike was trying to sell me his new PS3 games for $15 when he bought them for $60 Wednesday. That's crackhead behavior right there.
This dude agreed to drink my piss for $5. If that isn't crackhead behavior, I don't know what is.