98% of negativity is shared during the DF (x-server team matching) runs. "How" is a good question, but probably is too complex to solve.
From my experience people start to share negativity after certain triggers.
1. You lost aggro, mob attacked me! - Well, don't loose aggro or don't use DF (either if you want to avoid this).
2. Not healed well or died. - Heal well and don't die. Later also dps.
3. Stop stealing aggro! - Stop stealing aggro, that's all.
4. You don't have a job! - Get a job before you reach lv35, or people will keep saying this almost every time they notice.
5. We wiped because you didn't do something! Truth is - most of content in DF (exluding EX) can be completed by 1/2 of roles present, so they just ask you to carry them. - Carry them or leave.
6. Your gear is too low! If duty finder allowed you to enter your gear is not too low, again they just want to be carried by you. Carry or leave.
7. Why didn't you know how to speed run and wiped us? - Not sure about here, i personally do not attempt to speed run in DF and leave if team insists (30 min of waiting is better than 30 min of wiping + all insults).
8. Skip scenes! - Get a PF team or skip all scenes but the after-last-boss scene (ask which one is the last), later can watch them in the innkeeper room.
9. Troll. - Ignore or leave.
10. U no stoneskin me! - Just leave, save time, they are beyond salvation.
I try to avoid these triggers as they seem to proc in 90% of occasions.
