You dress up in the Wolverine outfit (comic book version, of course) and when the priest says "If anyone objects to this union, speak now or forever hold you peace." The person busts into the wedding and causes general disarray. This is usually done in groups so as to cause maximum confusion.
Groom: Yo, I was just about to get married to the life of my life and you won't guess what happened?
Groom: Joe, Phil and Harry came in Wolverining...
Priest: If anyone objects to this union, speak now or forever hold you peace.
Wolveriners: Yo! We're Wolverining this wedding!