Used to signify somebody trying to leave a conversation or to indicate a sudden celebration
"Oi, so me mum is cooking some poptarts, you want to come over for a bite and to watch some Hotel Babylon laterz?"
"And there's the johnny be good." *leaves rapidly*
"Oi, so me mum is cooking a big fat steak and we're going to watch the new episode of Dr. Who, you want to join?"
"And there's the johnny be good." *jumps for joy*