Once he's in London, Joseph Andrews parties hard. He never gets too crazy, but his ability to let loose makes Lady Booby get even more attracted to him.
One day in Hyde Park, Lady Tittle and Lady Tattle come across Joseph arm-in-arm with Lady Booby. That's some major scandal, if we do say so ourselves.
Joseph doesn't really get the implications of why this is so bad. He's a pretty simple fellow at heart.