r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.
My suggestion: say “Hi” while looking at them; only introduce yourself to them if they say “Hi” back while looking back at you, and with an enthusiastic-sounding tone of voice.
(Myself, I go by Postel's Law here: I don't initiate conversations with strangers on a plane, but don't freak out when they initiate conversations with me either.)
I think sitting really close beside someone I would be less likely to want to face them - it would feel too intimate.