There's at least two distinct levels of badness.

Some people try to play the game to the best of their ability but for some reason end up being bad at it. Maybe they have laggy internet, an underspecced computer, a disability, or are just overwhelmed by all the simultaneous mechanics.

Then there are those who apparently choose to suck at the game. Tanks that stay in DPS stance and don't hold aggro, healers that only use their most basic healing ability in Lv70 content, players of any role who don't make the slightest attempt to move out of any AoE.

A special place in hell is reserved for those who exhibit some form of inexcusable badness and proceed to blame others for it.