“That’s intriguing.” For strange situations where you are o_O at some of the, uh, radical phrases people say in public.
“Fascinating.” For difficult situations. The Spock affect always breaks tension.
“Puke City.” For those days when someone has the gull to use the crudest vulgarity in speech or action.
“Look! There’s a ______ behind you!” When I really want to get away. It works in the movies and real life. :)