She may think it’s a complement referring to an expensive Starbucks cappuccino, but it really means she’s pretty and popular on the outside, but she’s a rabid bitch on the inside.
b) It's a term used to describe a girl who may look cute and sweet, but she’s really a rabid bitch from hell.
Mean Girl: I was just kidding about you being a beast.
Victim: Aww, you really are frothy and delicious.
Mean Girl: Thank you!
Guy 1: How does a girl turn into Bridezillas?
Guy 2: She starts out cool, but watch out, deep down she's frothy and delicious.