Builder's bum 

When someone in loose trousers bends forwards and the arse crack rises above for all the world to see.
Common with builders, council workers, plumers and general overweight people.

"My plumber was fixing my pipes and his swetty builder's bum kepted staring me in the face."

Builder's bum by Mr Yin January 6, 2009

Builder's bum 

When a bird bends down and the top of her arse crack is on show

If she bends down any further she'll flash her builder's bum

Builder's bum by MK'chenko July 6, 2006

Builder's Bum 

a condition in construction workers where a fall onto a piece of equipment causes it to become lodged in the anus

A 31-year-old builder was left in agony from Builder's Bum, when a freak slip from a ladder thrust the handle of a shovel 20 inches up his backside.

Builder's Bum by eisiger May 29, 2011