The season's fourth episode, "Beryl," is when we really get a chance to see what Princess Margaret is up to. It opens with her at a friend's wedding, where she's clearly still nursing wounds from her breakup with Peter Townsend. Sensing her frustrations, longtime friend Billy Wallace spontaneously proposes to her at the reception. He says that it's better that she marry "somebody one at least liked." Although it's obvious that Margaret isn't over the moon about her situation, she accepts.
Flash forward a bit later to the day she and Billy are supposed to announce their engagement to society. It turns out Billy is a huge tool and stands his bride-to-be up because he got into a drunken duel the night before (that he lost, obviously). It's unfortunate for the princess, but luckily it gives her a reason to deliver this brutal takedown while he's pathetically laying in bed:
"People like you don't get to insult people like me. You get to be eternally grateful. Take a look at this face. A picture of disappointment and disgust. This is the look that every woman you ever know will come to share. This is what the next 40 years of your life will look like."
I really hope Billy immediately puffed into dust after this because there's really no coming back from a burn like that.