All these years and I never knew.
Ignorance reduced.
“All that stands between him and us is a thin layer of nylon!”
It looks like a handy place to store some energy-boosting carbohydrates. These riders look as if they have some bananas and plums stashed, in order to refuel on the go. [¿NSFW?]
From what I’ve read, the advice is to not shave.
When motorcycling, I wear bike shorts as underwear and motorcycling pants overtop. Occasionally I’ll wear non-padded compression shorts underneath. Never occurred to me to put anything under the bike shorts since they fit like compression shorts, which are basically athletic underwear.
Being that brevity is the soul of wit, I can do it in one word: Craft. 
This photo of a women’s cycling team would appear to contradict that advice.
I believe this should be labeled NSFW, at least if it’s real, or unless I’m being whooshed.
[rant] Just a note, but I grew up bicycling in the mountains on a 20 mile course, every week or so, through the summers. What did I wear? Plain ol’ shorts and a t-shirt like real humans wear, and so did my parents, and so (presumably) did a couple of generations before bike shorts were invented and popularized and no one was complaining about chafing and all this nonsense.
Unless you’re in a professional race, and every millisecond counts, just wear frickin’ clothes. If you’re bicycling for exercise, trying to be aerodynamic runs counter to what you’re trying to accomplish.
If you’re not in a race and you’re not a professional, then wearing a bicycling outfit makes as much sense as putting on a sports racer’s getup because you’re driving to the next city over. [/rant]
I can’t be bothered with doing much prep for a bike ride, so I’ve never bothered with bike shorts (or shirts). I just get on my bike in whatever I’m wearing at the time, which at this time of year means cutoffs and t-shirt.
Considering that the OP experienced chafing, this rant is misplaced. And I’ve certainly gotten saddle sores while cycling with regular shorts. Also, note that because of where saddle sores occur, people often don’t mention them in public or to people of the opposite sex, but they may still have them. It’s possible that you even got them but didn’t connect them to your cycling wear.
Agreed. The purpose of tight-fitting bike clothes is to reduce chafing. If you can ride all you want in street clothes, fine. But to suggest that to someone suffering from chafing is absurd.
I too used to ride in regular shorts all the time, until I started riding metric centuries (60 miles) and week-long tours. I quickly learned that for riding more than 2-3 hours, lycra shorts provide a definite advantage over street clothing.
And not just the bib (in my case), but the jerseys’ material. It keeps the sweat off you and dries quickly. Comfort is key.
I often do my mountain biking in tighty spandex shorts, but I also have three pair of mountain bike shorts that I wear as well.
The older pair I have has an undergarment sewed into it, attached at the waistband. The undergarment is tight and has the padded butt thing.
One of the newer pairs I own has something like that, but the undergarment snaps to the waistband of the outer garment. The other newer pair is just the outer garment and assumes you’re wearing your own undergarment.
With both of these, I just wear the sports kind of tight, non-cotton underwear. I don’t need a pad for mountain biking
Yup. I’m now educated. Admittedly even with my previous ignorant behavior chafing decreased after I acclimated within a few longer rides but the bunching up is nice to avoid. Doing half centuries plus with underwear bunching up was just dumb.
Agreed that cycling wear is not much benefit for an errand about town, but when one is cycling as exercise, getting your heart rate up there for a prolonged period of time, sometimes multiple hours, working up a good extended sweat, used correctly (not like I was) they can aid comfort.