stomp on his foot when he does the chest bumping try to make you flinch thing, this will make him lean forward and loosen his stomach muscles, hit him right under the ribs with a uppercut, put as much strength as you can in that punch, this will knock the wind out of him and make him lose all will to fight, if hes a real determined bastard then hit him a few more times, i have actually done this many times and it has never failed me.