5

'A limerick has five lines, with three metrical feet in the first, second and fifth lines and two metrical feet in the third and fourth lines. A variety of types of metrical foot can be used, but the most typical are the amphibrach (a stressed syllable between two unstressed syllables) and the anapaest (two unstressed syllables followed by a stressed syllable). The rhyme scheme is usually AABBA.

The first line of a limerick traditionally introduces a person and a place, with the place appearing at the end of the first line and therefore establishing the rhyme scheme for the second and fifth lines. In early limericks, the last line was often essentially a repeat of the first line, although this is no longer customary.'
Source: http://en.wikipedia.org/wiki/Limerick_(poetry )

A man once told me it was four,
I laughed and showed him the door,
I said don't be silly it's five,
Now get out while still alive,
Or your stupidity will end with you on the floor.

Five.

Here's one of mine.

I was going to blow, but I mightn't
Because it could make people frightened.
So my task is to see
How good I can be
As I was once told by Miss Deighton.

There was a young man from Dundee
Who was stung on the neck by a wasp
When asked if it hurt
He replied, 'No, not much,
He can do it again if he likes.'

Five. :)