Have you ever worn a t-shirt to play or jeans? Ladies, have you work a tank top without a collar?
I have gone golfing in a tank top once and was discreetly asked by staff to wear a collared shirt next time I came. I appreciate how they were tactful and didn't embarrass me with this.
I have worn a t-shirt before and it all depends on the course. But most of the courses I have gone to do require you to wear collar shirts. Which to me keeps it professional if you want to know the truth about it.
