Well it’s certainly not up to Mass-goers to impose their standards or imprudently tell newcomers or anyone else exactly how they should dress. If a man is dressed indecently, like a turning up in bathers that could be a different matter. But otherwise why do people try to impose dress standards that the Church herself does not impose?
BTW, there are other options beside the ones presented here by Lot who was trying to make it look like nothing short of a suit and tie is acceptable.