My personal favorite is the "Caution: Hot" labels they put on styrofoam coffee cups.
Yes, it's all about legal liability. For every stupid label on a product there was someone out there actually dumb enough to do the thing and try to sue.
I remember reading a story once where a character was able to get a "Warning - Do not stick in nose" warning printed onto grapes. It was printed right on the grape and on every single one too.
