I think our pool is just exceptionally abrasive.
Okay, okay, I know that the bit everyone's interested here is "how did you manage to scrape your lip on the bottom of the pool?!?"
The first thing is, I was swimming with my contacts in, so I had to keep my eyes shut tight whenever I was underwater. So I was gliding along underwater and I felt my trunks starting to slide down. I reached back to pull them up, and I think the change in profile caused my angle of attack to dip downward, and in short order I bounced off the bottom with the lower part of my face and my sternum.
No significant damage done in either case, just... ow! Pool, you are supposed to be a nice thing, don't be all scrapey!</i>