What should a 5 year old say to the response ' You look Stupid'?

from fellow clmates? He got his hair cut at the barber college last Friday. Its a little uneven and bowl shaped looking. Kids are ruthless. He had a perfect two weeks prior. I stopped him from going to Breakfeast and eating extra sugar in the morning. The teacher took his gloves and watch and complained this week that he was not following directions or completing his work. I responded that we complete all work sent home. None has been sent home. I am concerned he is acting up because kids are teasing him about his hair. What's the best way to handle this one...