I really don't understand just how on earth do you live to be middle age and utterly fail to grasp that clown pants and slippers are not a formal wedding attire? Sorry, but...how does this happen? Have you seen any photos from weddings? In the press, on TV, movies? You know, bride in a white dress, quests in formal smart dresses, suits, 2 pieces, men in suits/tuxes? And you whip out cotton clown pants with slippers and think, yep, that'll do just great?
My 12 year old is currently channeling her inner Kurt Cobain in ripped jeans, plaids and manky Converse. But even she grasps the concept of needing smartening up when going to a formal dinner in a restaurant/celebration, never mind someone's actual wedding..