oh maybe you don't know the phrase. not really either? closer to insane but the phrase "mad lad" is used as slang online to describe someone who did something that makes you say "damn i can't believe they actually did that. they committed to the bit so hard. they put in so much effort." stuff like that
It's not quite the same but I feel like "class lass" has similar energy. I also have a tendency to call my cat Lucy a "wild child" which also isn't quite the same