If they're not mechanical pencils then make some bite marks. So when he grabs one from you again, he'll be grossed out. But if it's a mechanical pencil take out the lead and if he asks for some just say you only got one piece left and your using it.
If you dnt have the nerve to come straight out n tell him no then only have one pencil with u at a time. You can keep your extras zipped up in your book bag or something and that will eliminate him taking them because there's none to take.