Well, I'm not much of a "potty mouth" but here are my favorite insults...
~Waste of human flesh
~Oxygen Thief
~Posterchild for Retroactive abortion
~You weren't hit with the ugly stick, you fell through the whole ugly tree
~Asking too much of your deodorant
~God made Oklahoma so even people from Idaho would have someone to make fun of
~Rip Van Winkle didn't get as much Beauty Sleep at you'd need
~You'd ugly a blindman to death
~Were you born and idiot, or is this just a midlife career change?
There's enough to get you started ;~D