When arranging my sister's wedding, either there was a cockup with the wedding cars or my DF had failed to think about how the bridesmaids (inc me, another sister and our young children) would be getting to the wedding venue. The car took Mum, him and the sister getting married and left. We didn't think anything of it, but then realised that a) they weren't coming back for us, b) that Mum and Dad had locked up and left us standing on their garden with the young children and that c) all other relatives had gone on ahead to the venue and we didn't have a key to get back in etc.
Luckily I had my mobile and was able to ring a family friend who was able to have a quick word in my Dad's ear and he sent the one car back for us. I never did ask whether it was supposed to take us first, or whether we were supposed to know to get our own way there, he certainly didn't mention it.
It must have looked weird for all involved for the bride to turn up in the car with her mother and father, then to stand waiting until the car went back for the rest of us! Luckily it wasn't far away.
Later in the reception, my sister decided to go ahead with the dance that she'd been taught at her dance/zumba hen do - which was danced to 'Britney bitch' and involved her flinging herself across the floor while pointing her leg at the ceiling!
In my own wedding, the vicar got my name wrong - repeatedly. DH wants to know if it's actually a binding contract.
At another, the venue ran out of food well before half of the guests had chosen their food from the buffet. And at yet another, the evening guests were arriving before the wedding lunch and speeches had finished because they were running so late.