Here’s my story:
About four years ago, my husband was asked to be best man at the wedding of a good friend of his, who happened to be a very strict Fundamentalist (a slight pause while everyone

how a strict Fundamentalist gets to be such good friends with a devout Catholic that he asks him to be his best man… hmm, done? Okay…)
Quandry No. 1–The wedding date happened to be on Holy Saturday. After conferring with a couple of priests and assuring them that it was to be a valid marriage with no impediments and that it was going to be a simple ceremony (DH was just going to wear a tux, hand the groom the ring, and sign the marriage certificate as a witness) with no kind of communion or any kind of worship service, and that these folk were adverse to serving any kind of alcohol and there was to be no dancing or music, he was given the green light to particpate (please note that the last would not have been a problem had the wedding not been on Holy Saturday.)
Quandry No. 2-- The rehearsal dinner was to be held on Good Friday. They were originally from Texas. They were planning a barbecue. DH called his friend the week before and said, “Look, I just want to let you know so that you’re not caught off guard, but we won’t be able to eat any meat at the rehearsal dinner. We will be there after our Good Friday services but this is a day of fasting and abstaining from meat for us. Please don’t worry about the dinner, please don’t go to any trouble to prepare anything different for us, I just want you to know so that you and your family aren’t offended if we don’t partake of the main course.” His friend thanked him for letting him know and assured us that there would be salad and… something that wouldn’t have meat for us to eat, but DH assured him that we would be fine. Well, bless their hearts, they made a pot of vegetarian beans, which the groom’s father made a point to stress the “vegetarian” part of it, probably so as not to scandalize the other family members and the rest of the wedding party with the fact that his son had chosen a
gasp 
CATHOLIC to stand up as his best man.
Then we went and blew our cover by making the sign of the cross when the minister offered the meal blessing.
Anyway, there were no hard feelings, the groom and his family were very understanding that we Catholics have, you know, some weird customs and, despite that, they liked us well enough to include us on this special occasion. And we’ve all lived happily ever after!