When a person's lips grant a facial expression of sadness when at rest or even when expressing joy. The lips fail to reach a horizontal orientation even when the person is attempting to smile.
Husband: Your mother looks looks so pissed off right now.
Wife: Nope, she is smiling.
Husband: Yeah, but she has a huge frown; it looks like an upside down U, like the old dude in Up.
Wife: Oh, that's because hse has the mother-in-law's contracture.