My own wedding where:
I walked up the aisle in a cloud of weed smoke because my heavily pregnant addict sister who was BM (I didn't want her to be, she didn't want to be, Mum made us) decided to light up a joint as we walked in. She also refused to have her dress fitted and wore dirty old trainers under her (thank goodness) floor length dress. As soon as the meal was over she changed into a tiny vest top and denim daisy dukes and sat with a face like thunder because I wouldn't invite her drug addict, jailbird abusive boyfriend.
My brother forgetting to bring dummies and snacks for his two daughters and looking to me for a solution (food I could help with, dummies I couldn't) and refusing to go to the open shop 5 minute walk away so all my family had to leave and go home with him (my mum had booked a minibus to take them the 60 miles home because none of them would pay for a hotel).
My nana asking me over and over to ask the DJ to put "Rocking All Over The World" on at the night do - as if she didn't have legs or a mouth of her own
A guests plus one who repeatedly asked me to allow her husband in (I didn't know her, let alone her husband and we were already at capacity) and when I said no, she got wasted on red wine, passed out in the toilets and they had to call an ambulance for her.
We'd booked the room until midnight under the strict instruction to stop the music at 11:45. We were halfway through the last song at 11:35 and the DJ turned off the power and flipped the lights on because he wanted to go home early.
My cousins girlfriend who used it as a stage to loudly push for an engagement of her own and loudly moaned about our cheap and cheerful wedding to anyone who would listen and told them all how she would do it differently (I got her back 8 months later when I announced my pregnancy at a big family event, stealing her thunder - she had planned to announce her own pregnancy but as I was 13 weeks, in my late 30's and had been trying forever, I got a lot of attention and she decided to leave it another few weeks as she was only at 8 weeks herself!)