Here's how it played out on a recent PHX-PHL redeye in FC. Husband and wife were sitting in 3D and 4C, both aisles. Kudos to the wife for sitting in her assigned seat. 3F comes on a little later and husband asks if he would be willing to switch with his wife, window for aisle. 3F respectfully declined saying he preferred the window. Husband was fine, said something like, "thanks anyway, had to ask." And that was that.

No dirty looks, no harsh words. Handled wonderfully by all three.