You don't know what Blood Rage is (no lie, I ran into a pug a while ago that ended up getting Blood Rage as the KroLord and no one in the lobby knew what was going on).
You play a level 20 Juggernaut on silver/bronze.
You bring a high-level Harrier TGI to bronze.
You think the Volus are the worst race to play as.
You get sync-killed every wave.
You equip the Revenant and the Crusader/AT-12 Raider on the N7 Fury.
You've never played above silver.
You refuse to kite sub-bosses and bosses when necessary.
You always use the Box of Shame on Firebase Rio.
You think that someone having high N7 always means that they're a really good player.
You think that someone having the BotB banner in the lobby always means that you'll extract on plat.
You play a level 20 character and get outscored by the level 1 that just dropped into the lobby.
You think promoting classes makes you a better player.
You only use the N7 Destroyer for the missile glitch.
You think that PPR is bad.
That's all I can think of atm...