I don't find it rude to occupy window-aisle with someone else in the middle. We're not usually chatty in-flight, and if we booked early enough, why should one of us have to take a middle seat when non-middles were available? Heck, more often than not, we're on separate PNRs for one reason or another. If we're settled before Mr Middle boards, he may not even realize we know each other.

On the off chance we do end up chatting a bit, it's *with* the middle-seat person, not over him. It happens naturally if everyone's in the mood to chat; otherwise we're quiet. Had one a few weeks ago where we had a pretty good time and bought Mr Middle a couple drinks in the process. But we've had others where everyone quietly read or used their own devices.

Granted, this is usually short-haul domestic. For something like SFO-SYD, we'd use miles for J where this isn't a problem.