I believe that everyone on the planet has some form of mental health issue. This combined with a competitive atmosphere can breed all sorts of unintended interactions. You get people that only want to blame others and never look to themselves, which probably reflects their true to life nature to some extent. You get people that are afraid to do anything period so lack of initiative/lack of confidence causes them to lose and get shit on because they "play safe", probably like they do in real life. Everyone that plays this game thinks they are a master of everyone else's role including their own, so thinking that you are smart isn't the same as actually being smart, most often times they are dumb as shit. Then you have the people that complain about everything then try to get you to listen or follow them, even though their actions throughout the game shows that they are anything but a leader to be followed. No one playing this game (below a certain level) actually cares about the team aspect of the game. People don't like being told what to do. People don't like to have their actions questioned. We are not allowed to flame them or call them out on their bullshit so they just continue down the same path cause we gotta treat everyone like they are a wittle baby, wah. Even if you tell people "don't fight, i'm pushing this wave first." the very next thing they will do, is fight, die, then flame you for not being there, even though they clearly saw you weren't there, then still chose to engage or put themselves in a position to get engaged on, then flame you for not being there. Fucking, mental.
My advice don't say shit to anyone. Period. End of story. Unless you are actual friends with that person or know them.
A lot of the player base is too immature to actually take constructive criticism seriously so even if you are nice, I highly doubt that will change the way they respond to you.
This is just my thought on playing this game for 3 years. It's always the same story when it comes to in game flame.