Yes, another question entered into Google and that landed on my website.
Question: "what do cowboys wear under their jeans?"
What kind -- boxers or briefs?
Question: do cowboys ever wear jeans without underwear?
Answer: I don't know. I haven't checked. But when I have ridden horses, I have required all the padding I could get between the saddle and my butt. I figure the same is true with cowboys. Underwear is a good choice. But you'll have to check for yourself, guys.
Also, remember, most cowboys wear jeans over boots, so you can say, in a way, that they wear boots "under" their jeans, too.
Life is short: ubi sub sub ubi (always wear underwear -- a Latin proverb LOL!)