My favorite (and I can't find the link) is the Reddit story from somebody's cousin's wedding. The groom didn't show up and didn't show up so, finally, in those pre-cell phone days, a delegation of male guests went to his apartment to see if something serious had happened.
The "groom" was rather surprised. He informed them that no, we aren't getting married; we aren't engaged; heck, we aren't even dating.
As I recall, the "groom" was known to the family, but was not close. The bride managed to convince people that he didn't show up for photographs or pre-wedding festivities because he was a doctor in residency whose schedule was too busy for such things.
Second favorite is the guy who showed up at his golf club ready to play a round, and walked into his own wedding, bride standing at the altar and all that. The couple were not engaged. The last thing the OP saw was the "groom" turning around and leaving with the bride running after him.