This is a trope where someone is set up on a Blind Date
— possibly by their friends, or family — and they assume it's going to be awful
. Maybe they think the person's going to be hideous (perhaps a few words about having a 'great personality' reached their ears). Maybe they've heard bad things about this person. Maybe they're just cynical about love and don't believe in it any more. Or maybe they just hate blind dates. For whatever reason, they go into the date expecting to be disappointed.
But instead, they get someone who is fantastically beautiful, or a force of personality, and they unexpectedly have a great time with them. The date is a tremendous success; this person is wonderful, maybe even — gasp
— their true love! This is this trope.
Named for a famous line uttered by Mary Jane Watson in the Spider-Man
comics, when she was introduced to Peter Parker in just such a manner.