6. When They "Genuinely" Couldn't Climb Stairs
The most famous joke in Doctor Who history was almost the most destructive when it came to the Daleks. It was always supposed that Daleks couldn't negotiate anything as tricky as a flight of stairs - according to one infamous Punch cartoon anyway - something that the Doctor himself played up to in the serial Destiny of the Daleks, in which the Doctor and companions escape from Dalek pursuers by he escapes them by climbing into a ceiling duct. The Fourth Doctor goaded the Daleks with a rather tongue-in-cheek "If you're supposed to be the superior race of the universe, why don't you try climbing after us?" - the same joke that was played out again in Chris Eccleston's famous, and rightly lauded "Dalek" episode, which finally showed Daleks ascending stairs. Subsequent revelations have established that the Daleks are far more mobile than once supposed, but still the stupid joke gets trotted out.
5. A Whisk And A Plunger
Another moment that fatally reduced the Dalek's impact: despite the fact that the Daleks make up for their mobility shortcomings with massive firepower that makes them genuinely threatening. Except to former Doctor John Pertwee who infamously and devastatingly said in a radio interview back in the 1980s that the Daleks were effectively glorified kitchen utensils...
"Doctor Who is OTT, you cant be serious, Daleks with sink plunger and egg whisks. Its very hard work. I didnt play Dr. Who right over the top, I played him straight."
Way to undermine your own mortal enemy, and establish an image that really, REALLY doesn't want to go away.