Remember, just one!
Absolutely it's "Tall Tales". Lady in Red, purple nurples, Sam and Dean in a slap fight, Sam recognizing alligator belly scales on sight and without any supporting context, "Dean, we don't have time for any of your blah blah blah. Blah blah blah--!"
Honorable mentions: "The Benders" for the grossness factor, "thinman" for effectively using the Ghostfacers in a pretty serious story; the titular half of "Beyond the Mat" for giving us a glimpse of Sam and Dean having unabashed and shared fun, and "A Most Holy Man" for giving us a fairly solid noir episode.