Easily one of the dumbest things ever (along with one-sleeved tops, those stupid beanbags for mobile phones, George W Bush and
the Slanket). Not only because your cat will develop severe neurosis, possibly resulting in Obsessive Compulsive Disorder, but also because it will make your cat hate your guts forever. Just try putting that blonde wig on Mittens, he will scratch your eyes out. Pop the silver one on Snowie for Christmas day, she will run away for days and come back pregnant.
Also, I'm going out there and saying it, I'm thinking that possibly $50 (USD) could be better spent on something other than a wig for an animal that is already completely covered in fur.
But, if you still want one you can buy them at
kittywigs.com and attempt dressing your cat up for your sick power games and entertainment. If the poor little bugger doesn't run away forever, it will make your life hell. Cats hold grudges, don't doubt it.