there is a reason they have weight classes in combat sports
Yes. That is assuming we are dealing with a trained fighter. If an overgrown bodybuilder slaps your partner's ass, you have just as much of a chance of beating him in a fight as he does you, assuming you are both untrained fighters. If anything, his lack of stamina and flexibility due to his overgrown muscles would possibly serve as more of a detriment to his ability to inflict any sort of harm on you. Having muscular arms doesn't necessarily translate into hitting harder. Guys like Ronnie Coleman or Kevin Levrone in their prime would hit much softer that any featherweight boxer on this planet. All of that muscle is a detriment to executing a proper punch.
Now, assuming the boyfriend is a skinny guy with a few months on MMA training under his belt, I can easily see him beating the living shit out of an overgrown bodybuilder that is not a trained fighter whatsoever.
Remember guys, in the streets once you find yourself facing an opponent who wants to bash your head in, you can't just start striking mandatory poses and hope that he would follow suit in order to beat him in a posing round. That guy will beat the shit out of you..
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