Stupid Bearded dragon.

[Beardedragon]

Is it possible he's seeing his reflection in the glass and trying to "fight" with it?

I thought of that too at first, but the OP does not mention him going black beard or pancaking himself out too, so I ruled that out.

Maybe he just wants some attention, or sees a Tv? I had a beardie that would glass dance when he was hungry, what all is he eating right now?

Could be space issues too, some people say a 40 gallon is fine but I think other wise.