I am not sure if it is peer pressure that causes males to not wear speedos in the U.S.. I think it is just the fashion in the U.S.. This makes them less likely to be sold in general clothing stores (Target, JC Penny, etc...) and as a result less people buy and wear them.
Hopefully that will change. I have found that men's underwear sold in general clothing stores in the U.S. is becoming more diverse (more brief and bikini types) over the past few years. This could transition into a change in swimming fashion as well
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