I speak in the language of puns, and it's all Joss Whedon's fault. Buffy and her crew may have been staking vamps professionally, but their stabbing wit is what made them some of the most well-written characters known to TV. Humor goes hand-in-hand with all that is BTVS and acts as a useful juxtaposition against the backdrop of horrors they all experience on a daily basis.
More importantly, the show emphasizes that we can (and must) find the humor in life, even throughout the most difficult times, because at the end of the day, we just have to laugh at how ridiculous it all is. Or sing about it, if a certain demon tap dances into town.
