My favourite limerick is so bloody racist that I can't reproduce it here. These two come high up the list though:

From deep in the crypt of St Giles
Came a scream that resounded for miles
Said the Vicar "Good gracious!
Did Father Ignatius
Forget that the bishop has piles?"


There was a young lady from Exeter
So fine that the lads craned their necks at 'er
And some were so brave
As to take out and wave
The distinguishing mark of their sex at 'er.