相席（あいせき,） means “sharing a table with someone you don’t know (e.g. at a restaurant)” (Takoboto).
What other fun words have you all encountered that just don’t translate well to English or require a short explanation?
I’d like to make a sentence that’s very long in translation, and/or read a silly sentence like that.
I can’t think of any off the top of my head, but might reply again later. You could also check out some 四字熟語, although those are more like proverbs rather than words. Eg. http://www.edrdg.org/projects/yojijukugo.html