Yeah receipt = proof. Applicable in many contexts
The thing about Bec is that her vile behaviour is so clearly driven my insecurity. No excuses but I think we'd see a very different Bec if Danny hadn't told her from the get go that there was no sexual chemistry and been clear that he's just not into her.
All her energy goes on pretending they are great at Commitment Ceremonies, dinner parties - even when they are alone in their apartment "We're great, aren't we?" and so on.
She is buckling under the weight of pretending to everyone (including herself) that she isn't hurt, rejected and embarrassed and it comes out as jealous spite. She would do SO MUCH BETTER to sit on the couch and tell the Ixperts, "Actually, I've fallen for Danny which is a bit embarrassing because I don't think he feels anything much for me and I don't know what to do with my feelings. Can you help me?"
She is equating Danny falling in love with her to her own self-worth. Am I not pretty enough for him to fall in love with? etc. So when it doesn't happen, the self-loathing is huge and she ends up sabotaging everything.
She's still a vile mess, but I feel sorry for her because it's so clear where it's come from.