People who take their shoes off on the plane. Why??
I get it, you've been walking the terminal all day, and your feet are sore, but that is still no excuse to take off your shoes on a crowded plane, especially if your socks or shoes aren't fresh. Further, if you are so disrespectful that you have to take your shoes off, don't compound this crappy behavior by resting your smelly, socked foot on the passenger next to you for any reason. Yes, I am speaking from personal experience in the last five minutes, and she actually thought I was going to accept her feeble "my feet are tired" excuse when I pushed her foot off my leg. This should be a fun flight...