That is the exact reason I took MA for so many years. I learned standup fighting fo 10 yrs and now going on 5 years of Jui-jitsu.
I would calmly tell him you heard that he wanted to fight and pick the place and time. I would tell him to bring all his friends to watch him get his ass wooped not once, but as many times as he has the stamina for. I would tell him that I need the cardio, and he will need the lesson......
I'd also make sure he had medical insurance for the compound fracture of his left elbow he is going to have at the end of the night......
TD