I know people who are self conscious about their arms, legs, or birthmarks or whatever and are always very careful to dress in a way that hide them. Most of them dread Summer because they will be met with constant comments of 'would you. not be cooler in a t-shirt, that top must be very warm', 'I could lend you a pair of shorts. You must be sweltering in those jeans', 'Do you not think it's time to ditch the tights until Winter'?
I remember, years ago, when I was very self conscious, being at the receiving end of some of those comments myself and really hating the first days of Summer.
So AIBU to think that people should stop commenting to friends or relatives about how they choose to dress on a Summer's day? They're probably feeling self conscious enough without you sticking your oar in.