Tiger says the offensive guest's date or family member is responsible for him and should be the one to address the issue as soon as possible: "As soon as they notice a problem, they should discreetly escort him into the nearest bathroom to splash cold water on his face or up to his room for an early bedtime."
White Washed
"One guest showed up at my wedding (which was very small and private, just for family and two or three very close friends) in an ostentatious, tea-length, white lace gown. Since I was just wearing a cream-colored skirt and jacket, she looked a lot more like the bride than I did."
Marlin says, in cases like this, there's no reason to worry. "The focus of the day is still on the bride," she says, "not usually the guest who is trying to steal the spotlight." Tiger suggests going with a comment such as, "Why, I thought you were the bride; how embarrassing for me and for you! Why don't you put this on so nobody else confuses you with the person we're supposed to be celebrating today?" Then hand her a sweater or a wrap.