Often heard in the order "badda bing, badda boom", the phrase is a
way of saying, "That's it, it's all taken
care of". The exact origin of "badda boom, badda bing" is a mystery, but the best guess I've heard is that it started as a verbal imitation of a "rim shot," the
drummer's punctuation to a comic's punchline in the old vaudeville routines.