WoW is a game of interaction. If you want to do any dungeons, serious PvP, or tough quests, you have to work with other players. Also like the real world, occasionally we meet other people we like, some we instantly click with, some who grow on us over time, and some people who just annoy the heck out of us. Sometimes it is in-game actions we find distasteful; sometimes it is how they talk to other players or any other variety of actions that hits a nerve. With some of these people, we have to bury our dislike because they are in our guilds, and we just do an if they don't bother me, I won't bother them approach. Others, we can avoid entirely and make use of the wonderful /ignore feature.
One of my biggest pet peeves is ganking. Killing someone who is 20 or 30 levels lower than you isn't honorable. It doesn't make you cool -- it is basically a grown man beating up a toddler. The worst part of it is that these same players tend to run and hide when someone their own level comes out to defend the noobs. This is a cowardly act. Another issue I have is people who use Xbox Live talk when they are frustrated -- they immediately devolve into racist, homophobic, and just awful and often nonsensical comments. My final pet peeve is people who mispronounce words in Vent but say them over and over as if it was on their word-of-the-day calender, pronouncing melee "mealie, mealie" and using it as if it were their new favorite word.
Are there certain actions other players commit that really annoy you? What do you find truly distasteful? Do you have some of these people who annoy you in your guild? Or are you one of the offenders?