Here, from Wiki, is the basic structure of the limerick, which we all know intuitively having grown up hearing so many of them… there was an old man from… etc.. Most of them, in fact, are off color, for example these dirty limericks, one of which is about Bill Clinton and Monica.
“A limerick is a form of poetry in five-line, predominantly anapestic[1] meter with a strict rhyme scheme (AABBA), which is sometimes obscene with humorous intent.[2] The third and fourth lines are usually shorter than the other three. The following example is a limerick of unknown origin.”
The limerick packs laughs anatomical
Into space that is quite economical.
But the good ones I've seen
So seldom are clean
And the clean ones so seldom are comical.[3]
Here’s another one from Wiki:
The limerick form was popularized by Edward Lear in his first Book of Nonsense (1846) and a later work, More Nonsense, Pictures, Rhymes, Botany, etc. (1872). Lear wrote 212 limericks, mostly considered nonsense literature. It was customary at the time for limericks to accompany an absurd illustration of the same subject, and for the final line of the limerick to be a variant of the first line ending in the same word, but with slight differences that create a nonsensical, circular effect. The humor is not in the "punch line" ending but rather in the tension between meaning and its lack.[14]
The following is an example of one of Edward Lear's limericks.
There was a Young Person of Smyrna
Whose grandmother threatened to burn her.
But she seized on the cat,
and said 'Granny, burn that!
You incongruous old woman of Smyrna!'
Here’s my Dirty Trump Ditty — uncensored because we’re all grown ups here: