its universally accepted that the fight begins once the shirt is off,
so the person who gets their shirt off faster generally has the advantage
in being able to throw the first strike.
It should be looked down upon. Either keep it on, or agree to start the fight once BOTH shirts are off. If you're going to fight to solve a problem, fight with some for of dignity rather than being cheap and beating the opponent to near death while he's on the ground and calling that "winning".
Why the need to take off shirts? Because for normal people, baggy clothing gets in the way during a fight...however 90% of hot headed "tough" guys feel that ripping their shirt off right as a fight is started is going to make them look tougher, make a difference. In reality, **** like this happens.