This is something I thought of a long time ago when I was really bored.
All you need is about 5 or 6 different colors of nail polish. Any will work.
If your one of those people who have like 600 different colors,
pick about 12-20 of your favorites. (It looks really neat if
they go together. i.e. just blue, red and yellow. Or all pastels.)

Step 1: Find something you can paint. I did this to a coffee table (painted silver) and 3 mirrors. But anything with a flat surface will work.

Step 2: Set all your nail polish in a reachable pile. (note: this is better when you do it with friends. One for each side of the object your painting)

Step 3: Seat yourself about a foot away from your object. (note: wear clothes you don't care to much about)

Step 4: Take your 1st color and get the brush really full of it. Now, this may be hard to explain. Take the nail polish brush (the one that comes with it) and whip it (yes, whip it) all over. The paint should make cool streaks and splatter all over. Repeat this with all your colors until your object is covered to your content.