for fun(also just for the fun of it) if you do something for fun, you do it because you enjoy it and not for any other reason
[TahlilGaran] Dictionary of Contemporary English ▲
for fun prep. phr. As amusement, not seriously, as a joke.
Let's try to play Beethoven's Emperor Concerto together, you on one piano, and I on another one. Compare: IN FUN.
[TahlilGaran] English Idioms Dictionary ▲