Barney's hot/crazy chart features the "Mendoza diagonal;" a girl below the diagonal is to be avoided. In baseball, the "Mendoza line" refers to a batting average of .200; a hitter below the line is having a terrible year.
Back in Season 1, in The Wedding (2006), when Ted says that Claudia is crazy, Barney replies that, to be fair, she is equally hot.
First introduction of an ongoing series gag of "eating a sandwich" (smoking marijuana).
Neil Patrick Harris would later star in Gone Girl (2014), in which his character have sex with Amy Dunne, who murders him during the act, hence fulfilling the Hot-Crazy Scale.