When Ron tells Kim that spending a whole summer away from her was the worst part about being at camp.
Dr. D's Villainous Breakdown, when you think about it. For the first time in his villainous career, Drakken put his best foot forward with the scheme he cooked up, sparing no expense in henchmen, stealing the best in nanotechnology from his nemesis' own father, analyzing every bit of research to help him understand the psyche of a teenage girl like Kim Possible, and refusing to pin any part of his plan on a Gambit Roulette like he usually does. The plan goes off seemingly without a hitch, world domination in his grasp...and it all begins to unravel by Ron Stoppable demanding bendy straws and completely falls apart the moment Kim regains her confidence and shuts down the transceiver. When you look at the rest of his open-ended, hare-brained schemes in Season 4, it really sinks in that this was the closest Drakken would ever get to ruling the world.