Many shops have a sign which is visible as you are leaving the store, which has "Please call again" printed on it.
Occasionally, when I leave such a shop, I do exactly what the sign says - I call out, "again!". Most people look at me like I'm a weirdo, but it's worth it to see the looks on the faces of the few who get it.
It embarrasses the heck out of my wife, but she lets me have my fun. Sometimes.