The other day I was in Karate, and my friend and I were doing Kumite(sparring) and my sensei gave me 20 push ups for wearing a wife-beater under my gi, and I shouldn’t have asked why becasue he could have taken offense and called it disrespectful, but I did anyway and he said the rule was that only girls may wear a plain white T-shirt under their gi. Is this some traditional martial arts rule or something?