Paddy goes to the Doctor, complaining that his constipation is so bad, he hasn't passed anything for a fortnight.
The Doctor asks his to drop his pants and bend over. After examining him, the Doctor leaves the room, and returns with a pick-axe.
WHAM! RIGHT UP THE ASS!!! Paddy wails in pain, then suddenly realises, there's shit everywhere! His blockage is CURED!!!
"Tell my, Paddy," the Doctors asks, "Do you happen to be working on a building site?"
"Tat's roight, Doc! How did ye guess?"
"Well, next time you go for a shit, DON'T use an old cement bag to wipe your arse!"