2. To engage in anal intercourse.
3. To get something by begging, or mooching.
2. Those fellows over there enjoy bumming. The taller one bottoms.
3. That wanker's always bumming fags off of me.
The latter tends to aggravate spectators more as it is a wholly warped and embarrassing way of attempting to make friends or stimulate a relationship with someone of the opposite sex.
One of the most hilarious technique of bumming is unanimously the 'facebook bum'. This occurs between two people over the social networking site, and can involve anything from a poke war to a full scale conversation on eachothers walls, ending in variations of 'loveee yaaa!! xxx'
Other ways of bumming include mysteriously laughing at someones abysmal joke, or exerting extreme physical contact onto those who you wish to bum (this may sometimes occur when drunk, in which case it is not bumming)
WARNING - attempting bumming can result in serious loss in respect.
"yeah, what a mess"