A metaphor that you shouldn't ever take literally. It's true meaning is "to have lots of fun". The word 'blast' originates from big. So now, when you hear somebody say "Let's have a blast!", you won't have to wonder what they mean. Because, they're trying to tell you that the next following days are going to be fun!
Tomorrow, I'm going on a Summer trip to LA. Oh my god, we're also going to the beach and having cocktails! My life will have a blast!
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.