I agree with Sassy...

by punishing these behaviors you are drawing attention to them, thus inadvertently reinforcing them. (increasing frequency of it)

Since your objective is to decrease the frequency, rewarding him for not doing it, or ignoring the behavior and redirecting him to something more productive would work better.

Example: My son's school district sent my son home with "pink-eye" last school year. He didn't have pink-eye. What they did was, everytime they would say, "Don't rub your eyes." My son would rub his eyes. (His thinking is probably, "Oh this?" and he rubs his eyes) After awhile they started to look pretty bad. But the staff wouldn't stop. So they sent him home with "pink eye". I got the drops, but the pink was already going away, just from being away from those that were reinforcing the behavior. I never used them (because I wanted to see if it was pink eye--and it was a weekend, where I still would have time to use them if it was) and it went away as quickly as it came. I didn't bother trying to tell them, because they would have gotten mad and likely taken it out on him.

With autism, almost everything is "reinforcing" positive behaviors, or "not reinforcing" negative behaviors. It becomes an art. But once you get it, it makes working with autism easier. (then the challenge is getting others to go along with it)