Blimey is a little cry of surprise — the sound you make when something shocks you, or when you cannot quite believe what you just saw. It is British, informal, and a bit old-fashioned in a friendly way. You hear it in films, from older speakers, and when someone puts on a Cockney voice. Americans almost never say it. You can use it alone (“Blimey!”) or push it in front of a comment (“Blimey, that’s expensive”). It is not angry; it is startled. Though actually, it is a polite hiding of a stronger phrase. People used to swear “(God) blind me”; that was softened and clipped into blimey, and you also get longer cousins like cor blimey and gorblimey. Some people say it comes from “blame me” instead. Either way, the sharp religious oath has had its edges filed off, so students can treat it as a mild “wow,” not as real swearing.