Want to tell people what you REALLY think? Then paste one of these Sti(n)ckers on their backs while they aren't looking. The set pictured is sold out, but you can check out a bunch more designs over at the Sti(n)ckers blog, or, if you live on the West Coast, they're available at two different locations:
GR2
2062 Sawtelle Blvd.
Los Angeles, CA (310-445-9276)
Giant Robot - San Francisco
618 Shrader St.
San Francisco, CA (415-876-4773)
[$20 approx., Comic Art Collective]