Previously the Orange Curtain referred to the border of Orange county and L.A. county but it is getting more commonly known and anything north of the 55 and the 405 freeways. The filth that is LA has reached down into such cities as Garden Grove, Fullerton, Placentia, Yorba Linda, and of course, Santa Ana. South of the curtain (cities such as Huntington Beach, Newport Beach, Mission Viejo, Irvive, etc) life is still nice and crime is low. Many people refuse to even cross this line because it takes weeks to get the stench out of their cars.
South Orange County is so beautiful and has just about everything but sometimes you just gotta cross the Orange Curtain to find a really seedy strip joint.