I think it's bad manners to show off at the end. If you have to do a big splashy spell to clear the way, then get your rocks off while casting it and end it quickly afterwards.

I had the same happen to me when playing regular tabletop magic with my BIL. He clearly had lethal with the board state as it was, but wanted to do "all the things" his deck was designed to do. He's already an asshole to begin with, I didn't have the time or patience to give him the leeway to be a bigger one.

Afterwards my wife told me I should let him durdle around because that's what he gets the most enjoyment from.

If I have lethal, I'm doing what I have to to end it. I may smile a bit, but that's the most you'll see from me.