I thought we had a thread a while ago, but I cannot find it now. Today I thought of a few:
"Put your hands in the air if you just don't care if you look stupid."
"Honk if you love my driving!"
"Flash your headlights if I am doing this right."
If you do not mind terribly, here is a completely unrelated bumper sticker that I actually made:
https://imgur.com/gallery/s2plG/new