WHU -v- Man City - Div 1 - 1987. You were already down, but at our ground in numbers for the final game of the season. First time ever I saw a set of fans invade a pitch, swap scarves and generally have a good old sing song. Possibly also the last, but it left a lasting impression on West Ham and City fans alike.
Man City -v- Palace one or two seasons later. My first visit to the Kippax. Still one of the best stands I have ever been on. You lost.
I'll chuck one in for my Spud cousin. Some time in the 90's. MCFC -v- THFC in the FA Cup (poss 6th round). Something got up your lots' noses. God knows what; its not as if you didn't make a habit of losing the important matches you played in those days ;] Anyway, it was carnage in the streets outside the game and he topped up having to beg a Spuds' supporters coach to let him on it (he'd trained it up there). Minutes later, half the windows went through and they ended up just flooring it through Manchester with the wind whistling through. Was only in his teens, but remembers it with a mixture of dread and adrenaline.
Oh yeah -
another 6th round game. Same old City. Home defeat aficionados...Look at the strike on that ball.