i smile to hide the pain
You grin like a fool to cover up your agony, people think you're nuts and always cheerful, but the more bull you get, the bigger your smile gets until you lose your mind over the smallest thing.
I smiled through the whole meeting, then yelled at the printer.
She laughed at my disaster, then cried in her car.
He grinned through the whole day, then exploded over a spilled coffee.