Providing you were straight:
You would generally call a fellow member of the same sex a 'Boot' for being stupid/an idiot.
You would call a member of the opposite sex a 'Boot' if they were un-attractive.
If you are not straight it would be the other way around! Both definitions could be used to describe the same person.
'Whys did jack do that?...He's a right Boot!' (Idiot)