I do public transport daily (as I don't have a car), so forget about planes. I have to deal with men spreading all the time on buses, and I always sit on half my butt if I have the isle seat so that no part of my body is in contact with the other passenger in window seat, be it shoulders arms albow butt legs foot. I am a man, and I find it uncomfortable to be touching anyone anywhere.
Yet, for some reason, most men seem to have no problem with sitting as close to me as possible, fully touching my arm elbo and my legs. If I move myself further away from the other person by effectively kissing the glass window, the other male passenger would move even closer to me to ensure every inch of me is being touched. I don't know what this is.