To throw up. Most commonly associated with excessive ingestion. Throwing up when you have the flu would not be booting. Throwing up after eating or drinking too much would be.
1) My ex-girlfriend booted all over herself at her birthday party. It was super funny.
A 'Boot' is a generic word for someone who is an idiot or un-attractive.
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.
'Look over there Adam....She's a right Boot!' (Un-Attractive)
'Whys did jack do that?...He's a right Boot!' (Idiot)