Here's one of my favorite "dirties" --

A maiden not otherwise crude, Once strolled down the road in the nude. A man came along, And, unless I am wrong -- You expected this line to be lewd.

This original "clean" won a prize from an Irish-American newspaper:

Maureen gave her doctor a sore shock When he tried to interpret her Rorschach. "This blot is OBSCENE!" She declared, "Well, I mean, It's a SASSENACH playing the clairseach!"

(Translations, if needed: Sassenach = Englishman; clairseach, pronounced "clahr-shock" = traditional Celtic harp)