Calvin and Hobbes: Calvin (sarcastically?) invokes this for a moment when his father tells him he [Calvin] needs to go to bed earlier so that he won't be so grumpy each morning; Calvin starts going around with an enormous fake grin instead.
Peanuts did this on at least two occasions with Lucy and Linus.
In one strip, Lucy showed Linus a cartoon she had drawn, and told him to laugh at it, even though he didn't think her cartoon was funny.
In a Sunday Strip, when Charlie Brown said he heard a TV commentator say that the world was getting worse every day, Lucy countered that she's a positive influence. She then ordered Linus to smile.
Lucy: See? With me around, everyone's a lot happier!