When something is so exciting, so completely enthralling that you are nearly dying of the anticipation. In fact, the excitement is so great that it is equivalent to the feeling of jerking off. As such, you are completely pumped by the idea of doing something on par with masturbating.
Bill-"Wait, we're killing a 30 case right after the concert featuring our favorite band of all time!?"
Frank-"Hell yeah man get excited!"
Bill-"That's gonna be the best day ever! I'm Jerking-Off Pumped about the whole situation!"
Frank-"You read my mind!"