I'm sure this will rattle some cages but, here we go....

1. A few of my pet hates in this game are:
"Lone mavericks."
They run ahead, go down, then complain that others aren't there to pick them up.
They complain that they need "heals" and expect others to give them a kit.
Its selfish gameplay.

Its a "team game!" It was designed to be a team game. If you ever bother to read the developers comments they tell you that the game will not tolerate "lone mavericks."
The game forces you to play as a team or you die. Simple

2. "Speed runners."
I really don't get it. What is the fascination with speed running from safe house to safe house? Whats the point? Playing a campaign means actually playing the campaign, not just trying to get there in 2 minutes. Speed running is boring and pointless; period.
It's one of the most annoying things players do. If you want to "speed run" go for it but for Heavens sake don't do it in a campaign where others are clearly not interested in speed running.

3. "Kit eaters."
People just don't seem to get it. It's not rocket science. There are four players so there are four health kits in the safe house. (Except of course where there are 8 health kits in some places.)
Some players are just selfish. They can clearly see that other players need a kit but they heal with one kit (sometimes 2) then take another with a total disregard for anyone else.
I recently played a finale with a dude who used 3 kits after taking 1 hit each time. He was healing despite having 60 XP. We hadn't had the first tank yet! Of course other players needed a kit but did he care? Nope!

4. "Trolls."
Infuriating to say the least. You're having a good game when a player joins, shoots everyone or throws a molly etc, then leaves. It disrupts the whole flow of the game.

5. "Noobs."
If you bought the game in the Steam Sale yesterday, please don't join "expert" campaigns.
Play on Easy or Normal for a few months to learn the basics first. Then progress to Advanced for a few more months. You need at least 200 hours on lower levels before joining Expert campaigns, imo. It's not that we don't like "noobs." I'm glad you want to play the best "Zombie FPS" ever! But, you're only embarrassing yourself and ruining our games.

6. "Maggots."
There is nothing that irritates me more than players who steal health kits from dead players. Newsflash!
They will respawn shortly and they can collect their stuff! Leave their damn kit alone! If you need a health kit ASK! Most respectful Expert players will heal you if you need it anyway.
In a similar vein, maggots also include players with green health who swallow pills knowing full well others are red and need them. Also maggots who refuse to give a player pills/adren after being healed by a player who has orange or red health! So selfish!

7. "Event starters!"
Another "newsflash!" There is no prize for getting everyone downed or dead because you cant wait 30 seconds for players to gear up or get ready for the event!
Those idiots who run ahead and trigger an event while players are still coming through the spawn points.
Be courteous before you trigger an event and ask "are you ready?" Wait for a reply from All players before you trigger it. You'll get a lot more respect from others by showing a little courtesy.

8. "Vocaliser spammers"
Players who spam voices or sounds in the game. It's annoying as hell! Stop it!

One of the best things about this game is that there ARE respectful players who understand how the game works. They help - rather than hinder - other players by playing as a "team!"
It makes the game so much more enjoyable and fun.