Insults:

Why don't you slip into something more comfortable...like a coma.
You are so dumb, you play solitaire...for cash.
You are so stupid, you'd trip over a cordless phone.
For those who never forget a face, you are an exception.
You have signs on both ears saying "Space for Rent".
You are so old, your birth-certificate expired.
If stupidity hurt, you'd go through life on a morphine drip.
You're as useless as a screen door on a submarine.
You're a legend in your own mind.