I've got a couple. Once, in Pathfinder, I was a level 1 alchemist and we were fighting our way into a warehouse to get some special packages. The guy who is keeping the package from us is standing on the otherside of the warehouse, and I am about to throw a bomb at him when he asks if I really think I can hit him from across the warehouse. Seeing as it was pretty far I didn't think I could, so I drank a potion of true-strike that I had and defiantly answered "Yes."

Then I rolled a 20. I rolled a total of 42 to hit as a level 1 character.

There was also the time very first time I played 3.5. I had opted to play a minotaur as other people in the group were playing as monstrous characters. Because of my character choice I disagreed with the dm less than ten seconds into my first game.

DM:"So you guys are Lost in the forest and-"
Me: "No I'm not."
DM: *confused stare*
Me: "Minotaurs can't get lost"