1. to cadge or scrounge. From the noun form bum meaning a down-and-out or beggar. This use of the word is predomi- nantly British.

Can I bum a cigarette from you, man?

2a. (British) to sodomise

2b. (British) to have sex with. A childish usage, popularised by the wigga comic Ali G and still in vogue in 2006.

The postman's been bummin' your mum!

3. to practise enthusiastically, enjoy. This usage, fashionable among adolescents in 2006 is probably inspired by the earlier sexual senses of the word.

She really bums that band.