This doesn't apply to DL but i will put this here, last year i was on an EI LGW-DUB flight and picked a window seat (i was doing as back 2 back, so i literally got off and did customs then went back around to the same plane).

This elderly woman was in my window seat. I figured it was only a 40 minute flight so i decided not say anything, but i quickly began to regret that decision:

1 - She was drunk and smelled of alcohol (it was 11am!).
2 - She took up both arm rests to herself.
3 - She tried on several occasions to get her phone out of her pocket, and rather than sliding forward to make it easier she put her hair in my face.
4 - She started badgering me for wearing headphones during the safety briefing even though i had already muted it and told the cabin crew who wanted to check (sorry, but an intoxicated person in an emergency is far more of a risk than someone wearing headphones listening to nothing)
5 - She then starts talking to me through my headphones after the briefing about why haven't we taken off yet, why is this flight taking so long, "maybe after brexit this flight wont be so busy"

When we landed the person in the aisle seat actually saw my face of frustration and let me go ahead of her to get away from the elderly woman. When we was on the LGW buses the same elderly woman was saying the same things to random strangers all over again.

Would it have been reasonable to ask her to swap seats? Yes, because that's what i selected and was printed on my boarding pass, and i figured a bit of politeness (even if done silently) wouldn't hurt. But after that experience i'd just get up after takeoff and move entirely.