"This is my playstyle" is a poor argument for being bad.

[Pells]

I'll add another to this: hardware malfunctions. One time in fractal, we had a scholar who was extremely slow on heals, and when DPSing only used Broil. We wiped once at the second boss, and another time at the last boss because he didn't use Leeches on the bombs. We mentioned, "hey man, you gotta remember to get the bombs off," to which he replied, "Yeah, my mouse isn't working well, so I'm having a hard time targeting people." When asked why he'd flag for an expert when his mouse wasn't working, "I'm not waiting around to start gearing up."

If he's using a mouse, then he has a keyboard. Targeting other players (in a four man dungeon) is keybound to F2, F3, and F4 by default. Broken mouse button doesn't explain this.