Wolfbasher well said. 
I went gluten free for a while to see if it affected my IBS (it did not) and I'm incredibly thankful I can eat gluten!
The idea of making gluten free friends (or even total strangers) feel 'bad' about their condition is so bizarre that I can't quite get my head around it.
I've read bit of the thread Reredos, but not all, so hope my advice is not just repeating what others had said! It may well be!
I suggest, take your own food where you feel comfortable to, check out things in advance so that your friends are not in any way inconvenienced by your condition. This is for your benefit not theirs.
Eat only what is safe to do so. NEVER eat anything you do not want to in order to make others happy.
If/when friends make fun of you for your condition I would personally speak to them separately (divide and conquer) and privately and explain that:
a) This is a real condition which affects YOU not them
b) This is your body and you will put in it what you want and only that
c) As friends you expect their support and not their ridicule
d) You are not inconveniencing them in any way when you are eating out and to be honest even if they were inconvenienced in catering for you when you visit them this is what friends do for each other
Please stick up for your coeliac disease affected friend if they start on her, or remove yourself from any conversations where she or you, or your food allergy, is being made fun of
And finally personally I would mentally remove yourself from caring what these idiots think!
Of course they can be fun, you have known them years, your kids know each other etc and you do not want to lose their friendship, but really do you care what they think? I hope not.
They can keep their opinions to themselves and as long as you keep healthy ignore. Smile and ignore, walk off and ignore, whatever works.
Your gut needs you to protect it but I would also say you need to protect yourself esteem in realising you are more important to you than these friends, who seem very juvenile! Picture them in your head as Kevin and Perry as you calmly say "Lets' not talk about food allergies again."
Kevin and Perry
Best wishes for a healthy, happy, fun Christmas.