No Shirt, No Shoes, No Service!

Today I picked up two of the 4FLEMZ from school and on our way home we had an interesting conversation. We were sitting at a stop light and two high school aged boys were running with their shirts off down the street. Thomas immediately noticed the boys and said, "Mom, is that really appropriate for them to be without shirts?" Yes, he used the word, 'appropriate.' I had to explain to him that they were local high school boys who were obviously on the cross country track team at RSMCHS and that it was OK for them to run with their shirts off. Of course the next question from Thomas was, "so girls can run like that too?" Ummmmm, my response to him was that it is not appropriate for girls to run with their shirts off. Tommy then gestures toward his chest and says, "is it because of these?" (You can now picture what he was gesturing)
By this time the light had turned green and we were headed in the direction of the local Jack in the Box. Upon approach, we see the boys that were running. They had stopped off at Jack in the Box and proceeded to put their shirts that were tucked in the back of their shorts on before entering the fine establishment. Now Thomas wants to know why they put their shirts on! Ahhhh.  A million questions from the inquisitive six year old. Oddly enough, I love it!
Would any of you like to explain to him why there is a policy of NO SHIRT, NO SHOES, NO SERVICE?