Honestly man, if you use facebook or anything like that. I'd occasionally make updates about how you feel with your beard/facial hair. Crack a joke here and there, but make it pretty apparent that you are happy with it and that is all that really matters.

I'm not even kidding my friend, if you do that, you'll find out real quick who you're good friends are. Good friends might crack a joke or two, but they'll understand real quick that you're happy with it, and they'll accept it. Those who just constantly nag and rag on you are likely not as good of friends as you might think.

In regards to confrontations in person. As a few above have said, just crack a few jokes about yourself, try to predict or one up anything you think they might spit out. I usually crack a Jesus joke, as He's my hero, so I can laugh for more than just the beard joke lol. But ultimately, its a matter of identifying your genuine friends from those who put you down to feel better about themselves.