In either the sauna or the steam room, Lots of guys at my club wear their gym shorts or swim trunks if they aren't planning staying beyond just a couple minutes. I've seen a few guys wear boxerbriefs that look like squarecut speedos or a very trim cycle short, but this is extremely rare and these guys are usually looked at with some sort of disregard by others in the room.
Most of the guys will wrap their towels around their waist and walk from the showers to the sauna, come inside, and sit down. That's where the behavior deviates: how the guy uses the simple white towel.
Some guys will lay their towel down and sit fully naked on it, fully exposed. Some guys will sit bare-cheeked on the tiles (steamroom) or boards (dry sauna) and instead lay their towel across their lap, draping their lap and legs for modesty sake. A few guys will sit on one edge, and flip the opposite edge into their lap to cover the junk, but leaving one leg/cheek fully exposed. I've even witnessed guys doing situps or bends, etc in there and that really annoys me- it's meant to be a place of quiet reflexion, not an extension of the workout floor.
Most of the guys I seem to sit across from will instead keep their towel reasonably tight around them, which creates the "kilt" look- and then they place their hands in their laps on their towels- usually right on their balls. Sometimes you sit at an angle (across from, above, below...) that means you look right up their skirt. Some guys are obsessive about eliminating any sightlines whatsoever. Others are oblivious to it. Some show off intentionally, others are so homophobic that you wonder why they are in their in the first place.
Depending on comfort level, some guys will come in and sit, and loosen the wrap at the waist as they sit, which will make it a bit more comfortable to sit without a tight wrap at the waist. This is the "norm"- however it can also mean that the towel may open a bit at the waist, which puts the undercarriage on full view to the guy opposite from you on the bench.
To be honest, if I know the guy I am sitting across from, or if I feel comfortable with him, I won't worry about what is visible if I am in the steam room or sauna. After using the same club for almost a year and a half at around the same time, most of the guys aren't strangers- and so I don't panic about my body. I might notice a buddy admiring my body, and while I don't FLAUNT I don't rush to cover up, either. It can be flattering or it can be a real turnoff really fast- it just depends on who is there.
It comes down to comfort. While there are guys my age and who are athletic fit/trim, there are A LOT of old, fat, disgusting and unattractive guys who I NEVER see actually working out. Instead, they are hanging out in the Sauna or Steam room like it's a gay bath house. When those guys are present, I either wrap up tight or I get up and leave.
It's not that I'm an ageist or an elitist, or that I'm arrogant. It's just a matter of comfort- I will show my body to whom I choose in the manner I decide, and I won't put up with a visual rape by a bunch of old men with no sense of self control. That's what makes me uncomfortable.
Sometimes I feel like there should be some sort of ticket required for entry and that you can only sit in the sauna/ steam room if you have worked out in the gym and earned the right to be there. That would change a lot of attendance at our gym- and what a great incentive to get fit!