I also despise people who just refuse to tap. My rule of thumb is, if i'm having a submission being applied to me, and I can no longer move/scramble/escape I tap.
Last night I was rolling with a local MMA guy, within 20 seconds I hit him with a kneebar off of x-guard, started puling it back, felt that it was about to go to the point of no return, and I look at the guy and he was just lying there looking me in the eyes.
Whatever, I let it go, and transition into a straight ankle, same thing, I get it fully locked on and start to go to my side and once again he refuses to tap. I just decided to play my guard game for the rest of the roll, but next time I'm going to go till I hear matte/tap/stop.