Most memorable mount moment for me happened at a convention back in AD&D. Our pregen characters had mounts to take us up into the mountains to the dungeon of whatever. When we got there, this dude pulls out his 2 handed sword and cuts his horse's head off. Everyone was stunned. I asked him why he did that, and he responded that the mount did his job well getting him to the dungeon. Rather than leaving him to a horrible death, he wanted to kill the horse humanely. After a slight mental readjustment, and the thief clearly instructing the cleric to heal him from dying if necessary, we entered the dungeon. After we completed what we were supposed to do, we came out to find a troll had slaughtered all of our horses and was in the process of eating them. Needless to say, the player wouldn't stop smiling during the fight with the troll...