4th Edition D&D Game
The party (all around 5th level) was on a ship sailing to somewhere. I played Aelar, a Wood-Elf Ranger, who despised being on boats. No earth to feel beneath his feet made him very uncomfortable. He was often in the crow’s nest because it was the closest thing he had to being in a tree.
After a day or two of sailing, an Adult Black Dragon comes swooping by (I don’t remember the story reason for this). It was probably out of panic that Aelar shot an arrow at the Black Dragon, and scored a critical hit. The dragon changed course and flew towards the deck. It smoothly transformed into an Elf-like humanoid before landing on the deck (so as not to tip the ship). Instead of being dragon-snacky-bits, the Black Dragon decided we were worthy to talk to.
The players later determined that I had, “shot off its nipple.”
Scoring a critical hit during a dragon fight became a common occurrence with Aelar (didn’t matter which d20 I used).
Then came a time that we were fighting a difficult enemy. One of the party members looked over at me and said, “Pretend it’s a dragon.” Dice rolled. Natural 20. DM frustrated.