Men and women who find the site of men wearing underwear sexually appealing have an underwear fetish. Seeing a man in his underwear has an intimate feel to it since underwear is generally hidden in everyday life. Often brief tight fitting swim trunks, such as Speedos, also appeal to people with an underwear fetish.
Some people with an underwear fetish find most or all types of underwear erotic where others find only particular kinds of underwear turn them on. Some types of men's underwear include briefs, boxers, jock straps and boxer briefs. Fabric can also play a part for someone with an underwear fetish. Materials like lycra and spandex are generally tight and form fitting. The man wearing tight stretchy fabric underwear or swimsuits tends to have the outline of their penis visible - a big plus for many underwear fetishists.