be (as) clean as a whistle

1. To be neat and tidy in appearance. This house needs to be as clean as a whistle before my mother-in-law gets here. I spent the morning scrubbing my bike until it was clean as a whistle. I don't mind Ella sitting at my desk while I'm out on vacation, as long as it's clean as a whistle when I get back.

2. To be well-behaved and not involved in illegal or questionable activities. You can trust a good kid like George—he's as clean as a whistle. I don't have a criminal record, I'm clean as a whistle. I hate to break it you, Paul, but Betsy has a thing for bad boys—and you're clean as a whistle.