I think that this is the mark of a very disgusting person.
When you're at a low point and you trust someone by showing them the tough things you're going through, the worst parts of yourself, your insecurities, your flaws, your weaknesses. When that person waits until you're in a different place and then throws those things back in your face - that person is evil, low, disgusting, and should never be trusted again.
I really, truly have always thought this and Bethenny is exemplary.
Say what you will about Luann, but she wouldn't do this to Bethenny. She'd bitch about the Fish Room and be narcissistic and self-involved, yes, but that's really the extent of her crimes.