Tell him to come at you first, usually when you expect a punch it's easier to avoid than you can hit him right in the jaw with all your strength, 90% of the time it knocks them down. Hit him in the face once more to get your point through and thats it, no need to show off.
Also to protect your mouth keep your right hand right next to your right cheek, and your left hand lined up to your left eye and about 8-10 inches away from your face. If you need you can jab with your left hand try to get him in the nose if he blocks it jab again and follow up with a hook to his jaw with your right hand.