My pet peeves:
*Players who use Greatswords with the arguement of: "well, my character would know that it could do more damage with a greatsword. I mean, if you put a 9mm Pistol next to a Self-Propelled Grenade Launcher and you wanted to do the most damage, you'd pick the Grenade Launcher. I mean, its just common sense. My character knows Greatswords are the best melee weapon for damamge."
*DMs who get to attached to their Homebrew that they keep it all in a lock box and if you try to explore in it, your are bluntly told by a building growing a huge fist and punching you for 3d6 damage to stop exploring and not to poke around. That was a true story of course.
*Players who cannot... nor try to, play any character (both alignment and mentality wise) other than themselves. Their arguement is "well, Neutral Good is boring to me. I wanna play Chaotic Neutral cause thats what I am. I wouldn't have fun as Neutral Good and thats the point of the game, to have fun right?" ........grrrrr
*Players (and sometimes DMs) who always take a negative stance with every NPC they come across. Example: "DM: You enter the grand chamber of the wizards tower, you see an old man working in the corner at what looks to be like a laboratory set up. He does not notice you." "PC: Hey you! Tell us where we can raise our dead friend! We were sent here to find something that can let us do it!" "DM as wizard: The wizard looks over to you kind with a shocked look on his face and says, "What?! Do you not understand that you are all trespassers on private property, extremely rude, and I could probably kill all of you with a wave of my hand?! This is my F'n house for crying out loud! Not a dungeon filled with monsters for your pleasure! NOW GET OUT! AND I HOPE YOUR FRIEND NEVER COMES BACK AGAIN!" .."Maybe if you were nicer next time, you'd actually be able to finish some quests!" He then goes back to working on some experiment."