I actually comforting / soothing for some babies to bite on things - especially around the age where their teeth are coming through or making a move. Have you considered getting him some new and different teething toys or mini icblocks to bite/suck on? I found this helped Elijah. I think it makes it worse when they think our reaction is hilarious but a firm no and giving them something else to bite is all you need. It can take a little while but they get the picture, especially when it means taking away their beloved boobies for a moment.