A Limerick is commonly defined as a humorous five-line verse with an AABBA rhyming scheme. An example of such:
Advertising is lots of fun
Others say it’s pretty dumb
Those losers know not what they say
I could advertise all dang day
So next time sometime says it’s dumb, let them know I have a gun.
You can find creativity anywhere - magazines, the internet, even poems. Take a moment to write a limerick or a haiku once a day, you'll be surprised what you can come up with.