Cachi is a derogatory term used to refer to douchebags and fratboys and certain bars or establishments where they might be found. Believed to have come from the character in Joanie Loves Cachi, the Happy Days spin-off. Girls of this variety are referred to as Joanies.
Some uses of this might include: "I don't like going to Jim's house because all his friends are so Cachi". Or it may be shortened to: " I don't hang out at those Cach bars downtown. They're so lame."