Translated as: "It's completely in the wrong direction!"
てんで = Completely / At all
方向【ほうこう】 = direction
ちがい = wrong
じゃない = is not
I'm struggling with doble negatives in japanese. In my mind I'd translate this as: "Is not the wrong direction at all!".
For the intended meaning, I wonder why is not correct to just say: てんで方向ちがいだ!
I'd understand that meaning if the ending was a question, as in: てんで方向ちがいじゃないの? , but this was not the case.