My own wedding.
I turn up at the registry office and my brother and his girlfriend (only family there, my mother - lives in Oz, couldn't afford to attend - insisted I invite him, I haven't actually seen him in 5 years. We are not a close family) are there by the entrance, first guests I see...both dressed in dirty jeans and sweatshirts, and my soon-to-be mother in law is plainly horrified. Wedding invite had said formal...my brother then tells me that they won't be able to stay long as they'd left their dog in the car (I have since realised that they weren't actually going to attend, and that the girlfriend basically forced my brother to go while they were out walking the dog, hence the attire).
Wedding ceremony over, I'm stood outside the registry office as guests are coming out, saying hello, posing for pictures, etc. Reception venue is at a hotel about 100 yards down the over side of the road, so guests start walking over. I suddenly notice that my brand new groom is on the other side of the road with a group of his friends, walking down to the hotel...I'm watching in disbelief as they disappear into the hotel. 5 minutes later, I'm still stood there, all the other guests gone, thinking like a fool 'he's going to realise he's left me behind and come back'...nope. I end up walking into my own wedding reception on my own. Groom still hasn't noticed I'm not there, he's too busy getting drunk with his friends...
My brother pisses off 15 minutes later. Good fucking riddance. That was 24 years ago, haven't seen him since.
Groom then throws a major sulk because he doesn't like the way his mother got the hotel to arrange the tables (she paid for the reception). Sulking to the point that other guests are giving him the side eye, and I'm hissing to him 'ffs, it's your wedding, you are supposed to look happy!'
The weather was vile, it rained all day - but that's to be expected in late November in the UK! I can still remember walking down to the hotel, thinking 'this was a mistake'...it was, we lasted a total of 9 years married. Ex husband hadn't really wanted to get married in the first place, he did it to 'shut me up' about it, as he charmingly used to tell his friends!