Kitten: "And would it kill you to smile?"
Robin: (forcing a "smile") "Maybe."
"This small fae has an almost maniacally friendly grin on its face".
— Pathfinder Bestiary II entry on Brownies
"The expression she produced was technically a smile, but it was one that belonged on something out of deep, dark oceanic depths."
There was nothing humorous or whimsical about that smile. No amusement. It was a thing of chilled steel—the smile of a wolf in the door to her den, between her young and the world as the hunting hounds closed in upon it. It was grim, hard, and yet, in spite of everything she'd just said, there wasn't a gram of surrender in it. For better or for worse, it was the wolf-smile of a woman who would die on her feet in the defense of her people and her home before she surrendered or yielded.
"THAT WAS A SMILE! I SMILED!!"
— Calvin, Calvin and Hobbes
...something flickered around Gryle's thin lips. It was a smile, panicking at finding itself in such an unfamiliar place.
He gave Dorcas and the the bandit a bright smile.
The bandit returned it. At least, he opened his mouth and showed a lot of teeth.
An attractive watchwoman behind him gave him a friendly smile. That was to say, her mouth was turned up at the corners and all her teeth were visible.
Step one: separate your lips. Step two: use facial muscles to pull back corners of mouth. Step three: widen your eyes.
This is how to be happy.