Before I even start reading that. I'm going to say - There's just no pleasing you is there when it comes to a job?
Editing coming after the reading.
EDIT: If you're going to bend over a take it with the unpaid overtime, then don't be surprised about how stressed you'll turn up. It's not showing to those around that shit can't get done in the time they've allowed for but apparently it can if you start working for free. Maybe give them an hour if you're feeling generous but apart from that don't bother.
Also, start making notes on what your co-worker does. Make note of times he says he'll do something, how long it'll take him to do it, how long you see him doing something else. So just in case it does go further you can say something like, "check the CCTV at these times" or just show your findings. I had a similar problem (more slacking than an authority problem) as he kept going to the toilet for ten minutes at a time several times a day, as well as going outside for a cigarette (which I don't have a real problem with, but he feels it's wrong if I sit in the back for a couple of minutes in return). As soon as he knew what I was doing he toned down the messing around.