Well, this seems to be the place for sharing anecdotes (which, I think, is the big pull of D&D - the ability to create shared moments that you can look back on, talk about, and laugh at).
There was the time the party was sneaking in to a goblin warren. The rogue volunteered to try and scout out the entryway, and slipped in. Sure enough, there were two goblins on watch. When spotted, he managed to kill both goblins before they raised the alarm. After this impressive feat of martial prowess (and lucky dice), he signalled the rest of the party that the way was clear by blowing his signal whistle (which the player had included on his sheet, and was looking for a reason to use), thereby alerting the whole warren who promptly swarmed out and mobbed him. After the party had rescued him, and beaten back the goblins, the paladin smashed his signal whistle.
Then there was the time the ranger decided to try and activate the mystic weapon-orb at the top of a tower under siege by the undead, because the party's wizard was being too slow and cautious. It activated, destroying the undead, but also blew the ranger off the top of the tower. He had the ability to reduce falling damage though, and survived the fall. Running up the tower to meet his companions, he forgot about the flame trap the party had avoided earlier, and got scorched into the bargain. Finally he stumbled out onto the towers roof, interrupting the party leader's impassioned eulogy.