Like "before I/we forget," "by the bye" means the speaker (or writer) is going to change the subject. It comes from "by" (meaning "near") "the bye" (the closing, where we say "goodbye.") So it means, "before we say bye, let me also tell you...."
"... and that's all I heard about Brenda and Eddie. By the bye, have you heard from Brenda's friend Billy?"
An expression of surprise and joy, by presumably referring to the nipples of a Babylonian god that were, for the sake of this expression, inordinately minty.
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.