Travelling in shorts in F class, whatever kind of shorts, is politically VERY incorrect.

CS PJs (PYE) are nice and easily washable in lukewarm water. We do it all the time. Why not enjoy one of the pleasure of F? The only reason I could see is if your friend is small size and you are large.

A lounge is a lounge. F lounge is not vastly better than J lounge. It is open to all DMs and the like flying Y, not exclusive. Once you have eaten and drunk (mediocre quality of wines) most of us get bored. Two hours gives you plenty of time to enjoy. On the return flight, I would simply ask for 2pm checkout from hotel, enjoy HK a bit more and head to airport by 7 to get some early dinner in lounge and a shower.