2. Something generally unpleasant.
3. The end of a spliff that has been stewing in the ashtray for longer than 18 hours.
2. "Gross, that stuff tastes fucking bumholes."
3. "The stash just ran out - all we've got left is bumholes."
The word 'bumholed' then became applied to anything that had been messed up, ruined or generally treated with disrespect. See example a.
You can also be 'a bumhole'. This is usually a person who not only treats things with disrespect, but scrounges off of others, takes advantage of someone or steals something. See example b.
Common 'bumhole' phrases you may hear are demonstrated in example C.
Ben - I can't believe that guy. He's been here for 6 months without paying rent, eats all my food and has bumholed my BBQ album.
Beth - What a bumhole.
C - 'Stop being a bumhole'
'Stop bumholing me'
'I'm sorry man, I've totally bumholed the last of your toilet roll'
'That bumholing bumhole has bumholed me for the last time'