They've gotten into some pretty hefty arguements if you can believe it. I installed the script recommended above and it flagged him/them not even ten minutes later. I took a chance and sent them a PM confronting them with this news and neither of them have logged in since.
If it really was two different people and this caused me to lose a nice guy along with the "not so nice" guy, I suppose it's a hit I'll have to live with.