Getting jiggy (with)
The entire decade was full of ridiculous idioms, but "getting jiggy" might just take the cake. Of course, the phrase has two connotations -- one merely implies dancing (see: Big Willie Style) while the other implies something seedier. This does not mean you should use it in either context.
The origins on this, uh, lovely term, are hard to pin down. Slang experts place it in the '90s, but it's not clear exactly where it came from. Credit might go to House of Pain, which referenced it in '92 on the track "Feel It." The line went like this: "And let's get down to do the nasty, freaky, funky, stinky, junky, let's bump uglies in the nighttime between the sheets." Considering "uglies" and "nasties" are kinda interchangeable, it's possible the members of House of Pain just started rattling off synonyms and landed on the phrase in question. Or someone might've noted that genitalia isn't that pretty before "Feel It" dropped. Hopefully, some noble linguist is on this very important case.