Etiquette

MvM has somewhat of a negative reputation for having an unfriendly community. I'm not going to sugarcoat it, you're certainly going to run into your fair share of unsavory and rude characters. That said, everyone should do their part to be as friendly as possible, and failing that, at least avoid conflict enough to keep games civil and free of headaches.

If people are outright being pricks, the best course is to not interact.

Yes, it might seem like a good idea to come up with a witty comeback or to beg people to not be toxic, but the truth is that there is no winning in an argument that breaks out in MvM. Nobody will want to admit that they're wrong or that they're being nasty. If someone is being an asshole, the wisest course of action is to simply say "don't be rude" and to not interact further.

Failing that, sometimes the unpleasantness that can occur in text chat or voice chat can be too much to ignore, and if you feel this way then the best choice for the sake of your sanity is to type voice_enable 0 and hud_saytext_time 0 in the console to hide all chat.

If you're new and unsure as to what to do, don't be scared to ask.

You might reasonably be scared of being called an idiot if you don't know what class to pick, what upgrades to take, or what strategies to use, but trust me that everyone would much rather you just ask than for you to make a bad guess. Chances are that there will always be someone in a lobby who has more experience than you and who will happily give you advice.

If a new player is making some rookie mistakes, don't blow your cool.

We've all been there-- everyone at some point has nearly lost their marbles at seeing a new player doing something that sabotages the mission, be it through spamming airblast or making a selfish dispenser. Yelling at new players and calling them nasty names, besides just being an uncool thing to do, tends to just cause them to be antagonistic towards you and to refuse to listen. The safest course of action when seeing a newbie make a bad mistake is to politely but firmly tell them what they're doing wrong and what they should do instead. Examples: "Please don't airblast the giants and Sentry Busters", "Please place your dispenser here where we can reach it", "Throw Mad Milk at the giants, please" et cetera.

Being a low tour doesn't make you not toxic.

Though the general consensus is that all high tours are dickheads (largely true), those relatively new to the game tend to be just as rude, selfish and entitled. Regardless of how much they subscribe to the meta, most players just want to do what they want and don't care about what the team needs. Yes, you'll certainly see people channeling their inner nazi simply because you picked Pyro or use the Gas Passer, but if people are giving you pointed advice about what you should and shouldn't do, you should remember that it's more likely that they're interested in simply completing the mission without any trouble more than they are in controlling you. So, please, don't get in a heated argument with someone who's begging you to stop spamming airblast and to not pop the uber Medics- just trust them on this one.

Press F4 as soon as you're able to.

Not to sound like a high tour fascist on this one, but if you have time to stand around on the front lines doing the Conga, then you have time to ready up. Generally speaking, it doesn't take too long to go back to spawn and to get your necessary upgrades between waves, so don't take forever to ready up-- especially if you're the only one who hasn't hit the button. Please.

You should use every chance your class has to support your teammates.

Tossing lunchboxes as Heavy, throwing Mad Milk as scout, throwing Jarate as Sniper, popping banners as Soldier, using the shield with Medic, reflecting crit rockets, keeping the Dispenser near everyone-- there's so many wonderful ways that you can keep your team alive and at full capacity. Remember that MvM is a co-op game, and that it's not every man for himself, despite what the general attitude of the community might make you think.

Classes other than Scout can pick up the credits, too.

Yes, Scout should be the one who's getting most of the credits, but it's a very busy job and he's bound to have his hands full most of the time. If he's not around and there's some bundles within walking distance, then you can help him out by collecting whatever's nearby and convenient for you to pick up.

Don't tolerate cheaters.

While going on a witch hunt for "cheater supporters" is a fool's errand in my opinion, it's incredibly easy to spot a spinbotting Sniper. You know, gun pointed at the ceiling, instantly killing every single robot as soon as they touch the ground. Just kick the blatant aimbotters, and if the rest of the team doesn't agree to kick them out-- leave the server.

Don't pop the uber Medics!

Deserves particular mention for being a common mistake with new players. Your team will more often than not have a dedicated Medic killer such as a Demoman or a Sniper, or in some rare cases a Soldier. Just wait a few seconds before firing on a giant so that its Medics can be killed first. If there are no Medic killers nearby however, then you can feel free to pop them early.

If you join a team without a Scout or Engineer, bite the bullet.

Yes, you might not want to play a support class, but a lot of people don't want to either. Someone has to take the short straw, and you should set aside your preference to play Soldier or Pyro if you're the last person to join a team without a Scout or Engie.

Play to win.

Some people join an MvM lobby with less than good intentions; some want to grief or to exercise petty authority, and some people want to join not to play seriously but to use "funny" meme strategies such as playing Trolldier, Fat Scout, or Battle Medic. In the case of the latter, allow me to assure you that every meme strategy that you can think of has already been done a hundred times, and you won't be causing uproarious laughter by dragging down your team. However toxic or not, the majority of players just want to beat the missions as efficiently and quickly as they can, without others starting trouble or throwing the game. It doesn't matter if you're not the best, or if you don't perfectly subscribe to the meta, the important part is that you should try your hardest to help your teammates beat the mission, even if you don't really like them-- and if you don't like them, you can always leave the server. Whether or not you're having "fun" is irrelevant if your idea of "fun" comes at the cost of others.