There are some things other PAX do that REALLY annoy me.
1. Ignore the safety briefing. Doesn't matter how many times you have heard it (and most have never LISTENED), it needs to be ingrained. Plus, it's only polite.
2. Ignore the seatbelt sign. Occasionally, I can understand that after take off and waiting for it go off, a toilet visit may be really necessary, but ignoring it completely is possibly slightly more prevalent on US domestic flights. It annoys me because such idiots are a danger to me if they go flying about the cabin as a result of turbulence.
3. Using mobile 'phones, blackberries etc. There's something to be said for fitting aircraft with mobile 'phone jammers. They wouldn't need a lot of power...
4. Not keeping the seat belt fastened when seated. If you hit sudden turbulence, unsecured pax flying round the cabin are a danger to others. Anyone not believing in CAT or sudden drops in altitude needs to look at the blood over the inside of the Qantas one that made an emergency landing in NW Oz the otehr year after hitting turbulence.
OK, I'm a miserable grumpy old fart!