Sometimes the heading bug thing can be more than just an irritating tic, it can be downright distracting. I was pilot-flying, autopilot on, in LNAV mode. We were in a turn and just given a climb. I began to reach over to turn the VS knob to initiate the climb, when the FO reached across my arm, blocking my access to the VS knob, so he could twist the heading knob. I'm trying to make the aircraft climb, and this guy insists on turning the heading knob, which, in LNAV mode will accomplish exactly...nothing.