What is a "bad player" to you?

[Kaedan]

Bad player is somebody who refuses to learn or adapt.

If your giving your best effort and at least trying to learn, I can be VERY forgiving.

This.

People who just do whatever they want without regard to mechanics or respect for other players they are with, and refuse to learn or communicate.

I like to differenciate between "bads" and "unskilled/inexperienced". The latter I'm more than willing to work with to help them improve. The former get on the blacklist and depending on the extent of their behavior, reported.