i smile to hide the pain
You wear a grin like a badge of honor to hide your misery, people think you're a lunatic who's always smiling, but the more nonsense you get, the bigger your grin gets until you lose your mind over something tiny.
I grinned through the whole day, then exploded over a messed-up desk.
She smiled like a fool, then yelled at the copier.
He laughed at my mess, then cried in the breakroom.