Whatever level of fan you fall into in the Buffyverse, it's always good to be able to spit out some Buffy jargon in case you ever need to kill Edward Cullen.
Something that Joss Whedon is remarkable at doing is creating new words. Some are simply just verbs or adverbs with a "y" tacked onto the end and used as adjectives. And some are funky fresh phrases or really shiny curses. Let's review some favorites from the Buffyverse, shall we?
1. Five by Five
This phrases was coined by the Buffy character "Faith." She generally uses it to mean cool or swell. "How are you doing?" "Five by five."
2. Big Bad
This is a term that I believe Willow might have started that caught on. It's a name for the main, evil villain at the time. It's especially helpful to use if you aren't sure exactly what the main evil is. "Come on, let's go take down the big bad!"
This is a more obscure word that means a "lie." Spike sometimes slips it into his vocabulary, along with "sodding, bloody, and pet." It's less noticeable when used though, because it's used in such a way that everyone knows the meaning of it without actually having to question it. Spike uses a lot of idioms and unique terms so we tend to just put together what he means without actually thinking about the words he's saying. "It's your own bloody fault for telling him a spin and then leaving him in the sodding desert!"
4. The Wig
"This place gives me the wigs." Another term for the willies or creepy.
5. The Hellmouth
This isn't so much as slang used in Buffy as it is a place known to all the mystical forces. However, if you ever hear something along the lines of "God this place sucks. We must live on the hellmouth." Note that this is indeed a use of Buffy "Slanguage." It can be used to describe a place that is less than ideal, hellish, or just simply a dump.
6. Prefixes and Suffixes
The most common words coined in Buffy, however, are simply words that have a common suffix or prefix added to them or are combined with other words. Focusy, stabby, slayage, wrinklies, uglies, guiltapalooza, and mopey are all some common examples of this.
Have fun gathering your own scooby gang and trading your own Buffy speak. Singing off!