My wife and I have been on 10 cruises, some long and some short, and most people are great. We still communicate with people we sat at dinner with years ago.
However, although we never "ran", we have had some unfortunate experiences - here are just a few:
--people who talk down to the service help and are rude to them for no real reason,
--people who won't talk to some others at the table (the reasons are unclear),
--people who complain about EVERYTHING. One couple was switched to our early seating table on day 3 who stated that the service was lousy at the late seating. BUT, every night thereafter they showed up at dinner an hour late (this screws up the flow of the service for the table), and while the man was a nice guy, his wife complained and complained, while everyone else at the table thought everything was fine!!
On our last cruise we got a table for 2. But we still got to meet some people at breakfast and lunch at large tables in the dining room.
But again, most people we have met have been fine, down to earth people (and I hope they felt the same about us).