To explain this, in Legacy of Time, you go to Shangri-La. There, you meet Ghengis Khan. When you walk the underground passages of the temple, you can climb up just behind him. If you do, he turns around and punches you back down the ladder. Arthur will then appropriately speak the immortal line.
Here, skip to about 3:40. Also, pretty much anything Arthur says.
(when trying to approach a person with their own Chameleon guise): "Can you imagine how that person would react if an exact mirror image walked up and said 'Hi!'...Well...I guessyoucan."