A Poem is the poem that Patrick flashbacks to reading in school. It's read during the episode Sing a Song of Patrick. After it was sung, Patrick was hit by dodge balls "just because we were playing dodgeball!".
Technically, it's not a song, but it still counts.
A Poem by Patrick Star Roses are Blue. Violets are Red. I have to go to the bathroom (swallows paper and burps loudly.)