Insults:

You are so old, the candles on your birthday cake raised earth's temperature by 3 degrees.
You are so dumb, you planted a dogwood tree and expected a litter of puppies.
Your house is so nasty, I tripped over a rat, and a cockroach stole my wallet.
Is your name Maple Syrup? It should be, you sap.
Your house is so dirty you have to wipe your feet before you go outside.
I heard your parents took you to a dog show and you won.
You're so dumb, your dog teaches you tricks.
Some drink from the fountain of knowledge, you just gargled.
You tell people you live just up the street from the corner of Walk and Don't Walk.
You are living proof that God has a sense of humor.