I'm not exactly built for t-shirts - I look like a double duvet stuffed into a pillow case in them!
My Group Sales Director is still of the totally outdated opinion that all salesmen should wear sharp suits (we disagree totally on this, but at least it gets me out of wearing t-shirts or polo shirts!) so nobody at my dealership does.
My delership seems to live in the grey polo necks. I suppose they don't show up the mould so well. I'm in the service industry and feel pressure to wear a suit but the temperature is 90 degrees and I look like a damp fish, not pleasant.