In reply to Firestarter:
In general I think it's good to point out bad practice, however several years ago (10+) when I was climbing with a friend, a member of climbing wall staff interrupted my knot tying routine to correct something on my partners harness.
We both stopped, listened, corrected it and then got on with our climbing. It wasn't until I was lowered safely back down onto the floor that I went to untie my knot and noticed I had only fed the first part of the rope through my first eight without finishing the knot off. The bottom loop of the first 8 holding only the bunched sheath of the second feed-through.
I was amazed (that I didn't fall), embarrassed (that I hadn't done my safety checks) and impressed (that the rope 'worked' so well) all at the same time.
I think if you're going to interject then be careful not to interrupt at a key point. I'm not blaming anyone except myself, but other people 'interfering' with your routine can be very off-putting, especially for beginners.