(just) for the fun of it
For no particular purpose or reason; only for the sake of fun or distraction. People don't call me Mr. Green Thumb for the fun of it! There's a group of kids who go around smashing car windows for the fun of it. Just for the fun of it, let's order dessert first.
for the fun of it
just for the entertainment value of doing it. We went on a picnic just for the fun of it.