"I still have two more layers left to strip." basically means "This isn't even my final form."
Scouter is definitely busted for giving tomboy friend such a low score! How do you even scale it, man? It should work on guys as well, right?
That's not a popular meme in Japan, their equivalent is actually the opposite. "Just five, trash." is the one that's popular in Japan and got referenced in this chapter. The one from when Vegeta first landed on earth and measured a farmer IIRC.