There was one bloke (I only ever saw him once), who did some press-ups on the mat, got up, walked across the gym to the mirror, studied his face closely (maybe squeezed a spot, couldn't be sure from where I was), back to the mat, few more press-ups, back to the mirror, check his face again, and so on.
It was as though he thought no-one else was there.
The ones who make me wonder the most is the (mostly) girls who go in there, spend twenty minutes or so on the bike/crosstrainer/stairclimber but put NO effort into it at all.
Yes, it's better than sitting on your bum, but if you've taken the time to go to the gym, why not at least raise a sweat? Get a little out of breath?