I'm pretty happy as long as there's only one way they can move a control to cause real grief - for instance you can easily block left pedal and forward cyclic in an auto without interfering with a student's practice.
The tough ones are things like hover autos (will they raise, dump or leave the collective alone? Will they push that cyclic in any of the four directions it can move? Stay tuned...) and slopes (same thing). Otherwise, mind your RRPM, altitude and airspeed, things aren't too bad.
Remember that no matter how experienced the pilot, throw them into a new situation and they may make the same whacko mistakes - just the other day in my EC120 transition I rolled the throttle on instead of off on shutdown (something I haven't done since I was a 20-hour pre-solo student). I'm not sure who was more surprised, me or my IP. I beat him to the fix, and no harm done, but just remember, they (we) are ALL trying to kill you (or at least your helicopter)!