Retard
Bitchtard
Where the hell is fucktard!?
Go look in the mirror.
Spoiler:(Sorry, that was too easy...)
Which is your favorite word?
Dotard
Retarded
Mitard
Fatard
Sotard
Latard
Titard
I usually just go with plain ole 'tard. It's nice because it leaves things open to interpretation by the insultee.
moetard