14:27 Jul 15, 2011 

To me it is a very idiomatic expression (indeed a cliché) in the form "to be/remain on one's best behaviour", but I don't think I've heard "on one's good behaviour". "As long as you remain on your best behaviour", or "As long as you behave yourself", or "As long as you stay out of trouble" (which is not quite the same but nearly): these, to me, are the things people (judges or otherwise) actually say.

13:43 Jul 15, 2011 

You're right, Mike! It's not as common an expression as I thought. I googled it and all i found was "to be on one's good behavior," or "to be on one's best behavior." The judge put in the "remain" bit.

13:10 Jul 15, 2011 

Kathleen, maybe it is me (sound to pedantic to say, "maybe it is I"). I am not familiar with it, but there are a lot of expressions I don't know. I am only talking from my own experience. It sounds strange to me, but maybe it is actually quite common in some areas, if not all. Thanks for your clarification.

13:07 Jul 15, 2011 

Mike, "to remain on your good behavior" is an idiomatic expression. It is not "normally" anything else.