I lost it with my older kids. I believe I posted this story before, but they were brother and sister fighting in the car on the way to the beach. I missed the entrance to the lot, and the next lot entrance up the coast, was lined up and taking like 5 min. per car to turn left across the busy highway into the lot.
They were physically fighting, screaming and crying, literally the ENTIRE time..I can't begin to tell you how bad it was. I was begging them to stop (I would have taken them home, but my son was with us and it wasn't fair to him)
I couldn't take it anymore so I decide to park in that lot, which was a MUCH further walk to the water. By the time I set our heavy bags down my back was cramping. I just sat down on the sand and started bawling. They were maybe 6 and 9 years at the time. I went off, told them it was their fault I was in pain. This was around 7 years ago, and I still feel guilty remembering their faces when I was blaming them.
I talked to them about it later (they were surpringly good on the way home...lol)