I did watch it and I take it as, it's the ladette era, she comes across as an "I can give as good as I get" kinda girl (in the public's consciousness), but when it comes to it, she sort of crumbles. I suppose, yes a mature human being would stop goading her, but Hislop's persona is a bit of an immature schoolboy type. He looks quite pleased with himself here and is probably embarrassed that she hasn't been able to clap back but doesn't know how to stop, so just keeps going.
Not sure why I'm defending him but she should've just laughed it off for the patheticness that it is. Don't know enough about the boob job tbh. It does look very obvious, but he says "you kept it quiet" like it was some sort of secret, so if it was a "secret", it makes sense that she would be a bit miffed that it's now the butt of some joke on national TV.