Folkloric history of those "Calvin peeing" car stickers

This site explores the evolution of those annoying and ubiquitous "Calvin peeing" stickers stuck on truck windows all over America. Explores the variations and corruptions, includes an excellent photo gallery.

My favorite part: the "generate-a-Calvin-peeing" engine, where you select who he hates (la Migra? The Navy? Ford trucks? "Fat chicks"?), whether it's the real Calvin or not, then generates a sticker for you on the fly.
At left, the variant I probably see most often when I'm tooling down the freeway between L.A. and the border. OK, that and the "praying to Jesus" one, which actually does not involve peeing, rather, praying.

Link, Discuss, (Thanks, Steve)