Tempest in a B-Cup
My personal observation from the ladies' locker room at the employer's gym suggests most gentlemen have no reason to fear opportunities for arousal from bare breasts.
Within that environment, there are ladies of ages from 15 to 75. Modesty is inversely proportional to age and attractiveness. The young women with beautiful bodies go to extreme measures to stay covered whilst changing, showering, and drying. The oldest ladies let down their "venetian blinds" front and back and proceed to visit with no thought to the view they offer.
If the attractive ladies cannot bear to bare in front of other ladies in a women's locker room, they probably will not remove their shirts in public. Hence you are saved from perpetual stiffies The real concern is whether you'll be able to function at all.
There are a lot of unattractive people in this world -- maybe we should all give ourselves an objective viewing and keep our clothes on!
Me? I'm old enough that if I LOOKED like those 20-somethings, I'd show it off. That's the dilemma of being in-between.