It depends to defend against or to play?
Depends on definition of opening. Worst first move is 1.g4 Grob.
Bird
THE PHILIDOR DEFENSE IT S*CKS
The Grunfeld and Alekhine blow!
The cow after just a few moves and no exchanges of pieces or pawns your score is -2.00.
Reti opening is the worst
Barnes Opening: Fools Mate.
WHY IS THIS NOT HERE???
Italian game because it has blunder