You need another bad habit (hopefully less bad though)
in the morning soak your fingers in vinegar for 5 minutes. this will give them a bad taste. not as bad as chicken poop but bad enough
Figure out when and why you are doing it, and chew on something else. Also, paint them with something that tastes absolutely TERRIBLE. You'll stop.
Why do you do it?
Try chewing them softly instead of biting through them.