I was on my Steam account having fun playing Team Fortress 2 which is a free multiplayer game btw and I was playing Man vs Machine as an engineer. Well to be fair? I'm not very knowledgeable in games when it comes to the role of certain classes in a game like TF2, but apparently these two other players didn't like the way I played and pinned the responsibility of me and the other engineer losing, so I decided to speak up and tell them chill out, but they continuously try to insult me. Since people say it is just a game, those type of gamers find it easy to possess those negative personalities on the Internet, similar to having a conversation with a friend on Facebook rather than doing it face to face in real life.
If you are in that type of situation where those gamers bother you, i would say ignore them and move on. I've been on Minecraft playing servers along with users acting inappropiately, but it hasn't affected me at all because I don't know who they really are in real life, and it's especially not a real life situation to deal with.
Hope this helps!
Also according to your update just quit the game and join another one where no players will be like that. Just a minor note that will help. A lot of the time these people are immature, young, or even both. Sign out In this world you find every kind of person. Some of the online gamers are lonely, pathetic guys who are frustrated from their life, thats why they are ignorant, obnoxious and defensive. Their lives are empty and lonely. To be honest, they are sad, loney humans that feel the need to bring people down with them.