%!&$ - Roll a critical threat followed by a natural 1
(DM) Like a ton of bricks - make the paladin fall
(DM) I never really was on your side - Convince a PC to turn against the party
(DM) - Roll up a new character sheet - Kill a party member outside of combat
(Wizard) I have a headache! - Summon a bee, then use a wand of enlarge vermin to make your monster grow
Holy Fucking Shit - Remember all buffs applied to you before your turn ends
(DM) How are you I'm fine and you oh I'm great how's the weather... - Make a scene where you simultaneously play the role of three+ NPCs
Badger Badger Badger Badger Badger Badger - Start playing completely inappropriate music during an emotional scene
(DM) It's only a social engagement - Convince the party to go to an event without armor/weapons only to throw an encounter at them
Om-nom-nom - Don't do anything useful during an encounter
(DM) Rage - Fail to stop out-of-character chatter for 20+ minutes
Holy Fucking Shit Bitch - Only roll a d20 once, regardless of where it landed or how low the result is.
(DM) One Page Wonder - Have your party totally deviate from the story within the first page of your notes.
(DM) Broken Lampshade - Have the players kill or ignore a plot-critical NPC.
(PC) Here's One I Made Earlier - Use a character you like and have been itching to use in a totally unsuitable game for them.
(PC) With Friends Like These - Down or kill an ally with a misplaced area-effect spell.
(DM) Critical Shit - Have your challenging encounter ruined by a lucky streak of criticals.
(PC) Critical Git - Have your character downed by a lucky streak of criticals.
(PC) Immovable Rods Don't Work That Way: Get into an argument about a minor rule for 5+ minutes.
(DM) Off The Cuff: Play through an entire campaign with less than 5 pages of plot/notes.
(Wizard) When In Doubt...: Kill 5 or more things with 1 fireball spell in the same round.
(PC) No Really, It's Original: Fool your DM into letting you play a character from an anime or video game without him knowing the source.
(PC) And Eat It Too: Kill an enemy using a piece of cake.
(DM) Unwelcome Guests: Run an entire campaign without using any DMPC's.
(DM) Not A Big Truck: Run a successful online campaign that lasts 3+ months.
(PC) Urist Would Be Pissed: Play a clean-shaven, sober dwarf with no accent.
(PC) Revolt Made Easy!: Successfully supplant the ruler of a kingdom without any citizens noticing.
(PC) Salvatore's Bane: Play a drow who isn't a neutral or good rebel.