In middle and high school for me in the US, the most popular underwear guys wore were boxers. The second most popular was boxer briefs, but you weren't considered a "real guy" if you didn't wear boxers. It sounds stupid now but when you're a teenager, it was a big deal. I used to wear boxer briefs, but since all the boys were wearing boxers, I switched over. Now I wear trunks and boxer briefs again.