Basically to me, two things.

-A player who refuses to adapt, listen or learn. You can be a fast learner or a really slow learner, that's fine. If you're willing to improve, you will make progress. If you refuse to improve, either by arrogance, putting the blame on others, expect a carry because "lul it's easy" or unwillingness to contribute, you never make progress.

-A player who refuses to offer help or advice, abuses other party members or is generally impatient, rushes because "lul it's easy" or leaves on the first wipe. This sort of player can have an Ultimate clear under their belt and be just as harmful or worse to the team than a new sprout who stands in the fire. They wreck team morale, cause wipes and mistakes by rushing due to other members being unprepared, ruin the focus of the group, contribute no help. You flat out don't want this type of player in your group.