I once refused to dive with someone in Tobago, as I'd seen them the day before on land, on the boat and underwater and, to put it politely, they were a liability.
Like a prat, I'd shown my DM card, so they figured they'd put him with me. He was a Rescue Diver, with some 50-odd dives, but that made him an expert, and he proceeded to grill me on diving experience and manhandle my kit. Given that I do more dives in six weeks than he'd done in his lifetime – plus my dislike of anyone fondling my kit without asking – I attempted to talk to him in a rational manner about the forthcoming dive (a fast drift down Kelleston Drain), but he just ignored any of my comments and generally acted like a tit. So, I refused to dive with him.
He didn't take my refusal to dive with him very well, and got all in my face and everything. I refrained from explaining that I thought he was a danger to himself and everyone around him, and instead just said we had different diving styles – and left it at that.
Anyway, said SPORE (Stupid Person On Rental Equipment) got loaded on to someone else, and I dived with a couple I'd been with previously, who were sound divers.
Predictably, 30 minutes into the dive, and the current suddenly picked up. Mr know-it-all SPORE panicked big-time, and the DM and myself had to manhandle him to the surface and back on to the boat. And guess what, he didn't have the good grace to shut his trap even then, blaming the rental kit (nothing wrong with it, brand-new Scubapro stuff), the strength of the current, even his hapless insta-buddy!!! It was all I could do from throwing him back overboard with a few weightbelts round his neck...
I dive on assignment once a month, and usually end up with a DM or someone to dive with, but ever so often I just dive with whoever is on the boat with me. I have to say that nine times out of ten, these people have been fine, but every once in a while I get one like the above idiot, and they are the sort who can cause serious problems for the people they are dropped on...
Mark