As a woman, I find it immodest for men to wear tank tops or go shirtless, especially with low cut jeans. I never know where to look. Away, obviously. I mean, if they look good, they shouldn't...and if they don't look good it's embarrassing.
Tank tops aren't as bad, but I hate it when men walk around in public with their armpit hair showing. Blech. Not something most women want to see in public.
Please wear a belt with a shirt long enough to stay tucked in when you bend over.
And too tight knit shirts are just as immodest on men when it's cold.
Skinny jeans, too, are not modest either. Same with the skinny suit pants that are so popular now, too.