In that mental (as in, You're mental!) is used to refer to the mentally retarded, this guy picked quite an apposite username for himself.

Doing little more than "pushing dose buttons" at mostly online casinos, this one can't see much beyond the projected outcome in the "hundreds of thousands" of hands. Can't grasp that it is possible that the short run, especially when it comes to risk of ruin, may deviate from the expected results of the long run.

What do you expect? He's mental!