Always wear clean underwear; you never know when you will be in an accident.
Don't make that face or it will freeze in that position.
Be careful or you will put your eye out.
What if everyone jumped off a cliff? Would you do it, too?
You have enough dirt behind those ears to grow potatoes!
Close the door! Were you born in a barn?
If you can't say something nice don't say anything at all.
Don't put that in your mouth; you don't know where it's been.
Because I said so!
Because I'm your mother!
(Feel free to add any others you remember. lol)