If they bicycle for exercise, then low tire pressure just gives them more exercise!
The thing that drives me most nuts is a squeaking chain. I once passed a guy riding a nice Trek roadie which was dry as a desert. Yes, I carry some tri-flow. He was making so much noise it was scary. So, we stopped together at an intersection, and I asked him if I might lube his chain a bit. He said fine, and I fixed it up. It sounded a lot better, but I am afraid he might have some permanent damage.
Anyway, generally I just let it go unless it seems dangerous. I led a group ride a few weeks back. One lady had 5 pounds in her tire. I had my Joe Blow Sport in my trunk, and inflated her tires to near the max on the side of the tire. She rode a lot better!