[KenWittlief]

I think the issue is the same issue with other public places (stores, malls, resturants, schools, churches, government buildings....) No shirt, no shoes, no admission. Its not a dress code thing, its a sitting-next-to-a-half-naked-person thing.

A tank top is a reasonable compromise.

EDIT: consider that it might also be a requirement of the venue that was rented for the event, esp if they are serving food.