In re-reading, I realize my post is not about bad buddies. But it is about diving with strangers, so I will post it anyway.
As someone who oftens travels solo, I have had as many (maybe more) strangers as dive buddies as I have had friends. I guess I have been extremely lucky because I haven't had any truly bad experiences. I can deal with an inexperienced or out-of-practice diver, as long as they aren't jerks or dangerously incompetent. I tend to be pretty adaptable and easy going.
In fact, I have met some great people as stranger/dive buddies!
In Cozumel, a guy from Oklahoma who was about my age (50 something?). On every dive, he and I were the oldest guys on the boat.....and also the last 2 out of the water, often after the younger divers had run out of air 15 minutes earlier! we loved it!
In Koh Tao, I was paired with a retired Frenchman who was worried that as an American, I might have an attitude towards him. When I warmly assured him that I was happy to meet him and to dive with him, we got along great. Turned out he was an instructor, and we were the 2 most experienced divers on the boat.
Also in Koh Tao, last month I was alternately buddied with each member of a nice Swedish couple. They were alternating days diving, so that the parent not diving could take care of their child. Both of them were super nice people and excellent divers.
1 day the seas were unusually rough. People were chumming off the back of the boat and having trouble walking on deck. The Swedish guy was reading a paperback as if nothing was happening! I asked him later what he did for a living, and it turns out he flies fighter planes (and others) for the Swedish Armed Forces! Small wonder the rocking boat didn't bother him! haha!
I have met many other cool people as dive buddies, but I have been long-winded enough, so I will stop now.
Thomjinx