A couple of ethical questions for you:
You are riding with your buddy and you see something similar to this:
Do you tell him his shorts are wearing out?
Now the hard one. You are a guy and the person with thin shorts is a woman. Do you tell her? And if so, how?!
Yes, this actually happened to me this year. I’m not saying what I did, but I’m still alive, so you may be able to guess.
The Vicious Cycle 
Good to see you grappling with the truly difficult issues of the day! I would reserve that sort of feedback for only the best of friends. Everyone else will have to manage on their own until one of their best friends helps them out!
Unfortunately I haven’t found a style book for cycling and I’m not sure The Rules address this one. It has to be addressed! Btw, I have naturally come to the same conclusion as you, so if I ever tell you you’re in need of new shorts, you’ll know I consider you a good friend!
Doesn’t matter who it is, I’d discreetly let them know at the end of the ride
That is a brave move, but smart to wait till the end of the ride!
I had a similar experience, was very torn about what to do but in the end said nothing. Which is probably why ten years later that woman is still my friend.
Interestingly, once while riding in a paceline the woman behind me gently suggested it was time to retire the pair of bibs I was wearing that day, a recommendation for which I was grateful.
You made the right choice, Christopher, as history has confirmed. I do hope she got a new pair of bibs, though.
you need a good friend sometimes .not always is mom around. Be a good friend
It’s good advice, although I’m still not sure the safest way if it’s a female rider.
Yes, if it’s a buddy I would tell them. It doesn’t matter if it’s a man or a woman if you know them. I’d bring it up either at some point during the ride or afterwards. I believe it’s much better to know and not have it happen again. If you don’t know, you don’t know! I’ve let people know, and also once had a mate let me know (oh, the shame, haha).
A stranger or somebody I don’t really know all that well? Hmm, that’s a bit tougher…
I sometimes wonder if my old shorts are ‘revealing’ and in my business this could be the difference between having a client return or not!
One of the good things about always riding alone is that these quandaries never appear. There are downsides though.
One downside is wearing a pair of bibs thin and nobody to tell you about it. Maybe Mrs T should give it a cursory look before each ride?
She does cast an eye over me from time to time to check that I am presentable.