Strewth is a short shout of surprise, shock, or annoyance — close to 'wow!', 'good grief!' or 'oh no!'. You say it when you hear a shocking price, see something amazing, or find that someone has done something foolish. It stands almost alone as a whole utterance: 'Strewth! Look at that!' It is very strongly Australian. Australians will hear it as their own, and it is one of the words used in films and jokes to mark a character as Australian, sometimes so heavily that real Australians find it a bit of a cliché. It was once common in Britain too but now sounds old there — something an older person or an old book would say. It is mild: no one is offended by it, though people who avoid religious language may still not like where it came from. Also spelled 'struth'.