On a different cruise line, we went to high tea in the big dining room and were seated with an elderly woman whose cabin mate died in her sleep the previous night and was being taken off the ship in the next port of call. This lady didn't seem phased by it as much as you'd think, almost like they planned it this way, and couldn't stop talking about her and all the things concerning her death (arrangements to get the deceased off the ship, visiting the deceased in the mortuary on the ship, etc.). Certainly the most awkward table mate pairing we ever had on a cruise. We avoided high tea for the rest of that cruise, sadly, as I loved their high tea service, but was too weirded out by that incident to enjoy it, even with different tablemates.
We've had some runners up though. Again on that same cruise line, we had some table mates who were guided to our table, they looked disgusted, and told their guide they demanded to be seated on the opposite side of the dining room. We were then given new tablemates, two divorced women who came to dinner only once and gossiped the whole time, and a couple from Korea who didn't speak much English and were only there for two of the seven nights. We loved our server so much that we kept the table and kept mostly to ourselves, which was easy when the other tablemates rarely showed for dinner. (We don't sail with this cruise line any more. Whilst we admired the service and the crew, we felt very uncomfortable and out of place with the other guests in general. My parents and cousins love cruising with this cruise line though, so maybe we're the crazy ones?)
Otherwise, we are frequently seated on our own (not by request) or we have delightful tablemates. On our honeymoon cruise the tablemates were lovely and caring and enjoyed talking about things they wanted to do in port or what they did during their day. Some of them offered to pay for us to come with them on a fancy excursion. (Sadly, we had something else booked, but we still had fun.) On our first
DCL cruise we were sat with two couples with young girls and had such a pleasant time that we kept in touch for several years after. One of the girls had similar allergies to me and we'd send care packages back and forth with new treats and goodies we found that were safe. We've had more great tablemates than weird ones, that's for sure.