Do something for a laugh/for laughs
Definition 1 of 1
Pro Tip 1/3Informal Use
The phrase is casual, often used with friends or in relaxed settings, not in serious or formal situations. 
They decided to swap clothes for laughs during the party.
Pro Tip 2/3Humorous Intent
It implies the action intends to be funny or to provoke laughter, not to be taken seriously. 
She answered the quiz for a laugh, not expecting to win anything.
Pro Tip 3/3Not Hurtful
The action should be harmless and not embarrass or upset others. 
They all wore crazy hats for laughs, nobody was offended.