You could sit next to a the nicest gentleman you've ever met, but if he smells, he is instantly your worst enemy. You think it was bad that one time you got into a urine-scented subway car? Imagine that for three solid hours. Whether it's body odor, egg and onion-infused farts, stinky feet, or good old fashioned stank breath, a flight without crisp, clean air to breathe is one of the worst things ever.