My FMIL was telling me yesterday that it's customary for the groom's father to be the best man. I've never heard of this. I can't tell if she means it or if this was some sort of way to guilt us into the fact that he's not in the wedding party, yet we are still requesting that he wear at tux. She's not normally that petty, but this is certainly something I've never heard of. I've been to like 20 weddings in the last ten years, and never saw the grooms father in that role. Side note: They WERE all wearing tuxedos though.