I'm getting closer to doing this every day. I've had KK vs. AA three times in the last few weeks and two of those times I had serious warning bells going off. The only time I didn't was against a short stack who didn't have enough money to set them off. (Also had QQ vs. KK in the same stretch, and also doubled someone up on it.) I've never done it yet and don't plan to make a habit of it, but I can see myself folding kings in one of these hands where me and a villainous nit both have 100 BBs and it goes back and forth a few times pre-flop. It will happen some day.