Posh trailed Cardiff 4-0 at the half time break but staged a remarkable comeback in the second half of Monday's game at London Road to salvage a point.
"We didn't get close to Cardiff, we didn't tackle, we didn't head and to be quite honest, we didn't do anything," Cooper said after the 4-4 draw.
"If you don't want to compete, you won't win a football match - whether it is in the local park or the Premier League.
"I didn't say a lot to the players at half-time - in fact, I thought about getting in my car and going home!
"But we changed our shape, changed our personnel and got ourselves back into the game.
"Cardiff probably thought it would be a stroll but we ended up getting a point, but I am still really frustrated that it took us until the second half to start playing.
"If we are capable of scoring four goals against a team chasing promotion in the space of 45 minutes, what could we do if we performed for a whole game?"