I sat next to this rude and fat black guy that smelled really bad and pretended like he didn't speak English. He occupied the arm rest for the entire flight, and kept bothering the flight attendants for more food. He wouldn't even move to let me go to the bathroom on a 8hr flight! 

Sat next to a bitch that would not stop coughing. The whole damn flight she was popping something and drinking water but kept coughing. Needless to say I got sick.

On a business trip I sat next to an older guy who proceeded to tell me loudly what was wrong with the world and what we needed to do to fix it. I didn't want to discuss politics, and I didn't want to argue with him in a confined space. When I learned to bring headphones if only to avoid the issue.

I only flew twice 11 years ago in a two-way flight between Puerto Rico and Florida. Don't remember the people beside me on the first flight, but there was this guy on the second flight who I ended up talking for a bit. I don't remember any terrible experience on those flights.

I sat next to an overtly homosexual man, who talked for the entire flight about not being able to wait to get home after such a long stint overseas and finally do some manscaping.

Not that I have a problem with such things, but it was an 11 hour flight and I was exhausted. There's a surprising number of ways to describe trimming your bush.

10 hour flight from Miami to Berlin. I had a headache on this flight and the guy next to me was farting all the time. I thought I would die.

The worst people I ever sat next to were the military crew of a C5-A Galaxy on a flight from Dover AFB in Delaware to Ramstein AB in Germany. The reason why wasn't because they were being jerks, far from it. It was because they were playing their Game Boys.

It was Christmas of 1989, and I'd just gotten a Game Boy, and we were flying to Germany using Space-A. My dad had been told I couldn't take my new Game Boy on the plane because it would interfere with the navigation equipment. Yet there were three or four airmen playing their Game Boys. :)

Same, that or with friends.

I absolutely hate those kind of people that be like "fuck everyone behind me, I paid for this and I'll damn well squish their knees/legs with my chair as much as I want". I hardly ever recline my own chair because I know full well what it feels like for the person sitting behind me. I wish airlines would just improve the seating space for regular paying flyers because even with the extra legroom doesn't seem to matter once someone starts to recline their seat.

I think the worst case I;ve been in is sitting in the middle area of the plane while there was a crying baby seated just 2 rows from me and another 4-5 rows back, both constantly crying on and off the the whole 8 hour journey to Orlando. I honestly don't know why parents bring their babies with them on holidays when most of the time they kick and scream and make a scene/ruin it for the rest of us. My own folks even said that they didn't take me to Florida until I was 6, my sister when she was 5 because they didn't want to go on holiday with screaming kids. I honestly don't even know why parents bring babies to watching films as well, it makes no sense because loud noises of any kind tend to set them off.

Long flight I was on and a Chinese family (mostly female and middle aged) refused cabin food but ate noodles or something a lot through the flight and were continually passing gas. Horrible....just horrible.

I sat next to a guy who smelled like beer and cat piss. To top it off the air conditioning on the plane went out, in June, in Phoenix. Fortunately it was only a 4 hour flight.