Limerick's are one of the most famous forms of poetry that have simple rules like

must have 5 lines

lines 1,2,5 rhyme

lines 3,4 rhyme

they will have a distinctive rhythm

they are usually funny

Author Anonymous

There was a young fellow named Hall
Who fell in the spring in the fall.
‘Twould have been a sad thing
Had he died in the spring,
But he didn’t—he died in the fall.