I have not played long enough to have anything like that but ive got a small one, here goes.

I am in an alliance which has very close cities. There was one member in the middle of us with 4 cities and about 150k prestige. He was not attacking us but we wanted a couple of his cities. However, he was in a much stronger alliance and so we held off. One day, he got kicked from his alliance and 3 of us took our chance and sent some waves on his cities. We all had fairly low feasting halls then so it took a while but it got to 2 and the member who wanted the city sent his final wave. 2 mins away from his target and conquering the city, the player joined another good alliance who just happened to be allies with us. And so all our troop losses and time had been effectively wasted.

Not as good as previous poster but thats all ive got.