At my gym where the showers are communal, all straight guys are checking each other dick and balls. I think it's an animal reflex, like dogs lol they are never looking for a long time but they are always having a glance. When straight guys are coming to a naked space with their genitals on full display they expect other male to look for every male in the room seeing they are also males.
From my experience, when straight guys are drunk they also love to show and look at each other dick. Not in a sexual way like gay guys, straight guys are seeing dick has something dirty/disgusting. But more as a way to affirm their manliness to each other.