This is a Teamspeak meme which translates to "I give up, I can not possibly win this arguement". If this is said during an arguement, the arguement is over as the person who said it has admitted defeat.
Person 1: One plus one is 3...
Person 2: Are you fucking stupid? One plus one is two.
Person 1: Not gonna argue wif u.
Person 2: That's what I thought.