This trick should be part of your solid wakeboarding foundation. When you've mastered the bunny hop, performing a 180 should be no sweat.
1. Learn to bunny hop (see "Get Air on a Wakeboard" under Related eHows).
2. Get comfortable riding in and out of the wake, jumping off it, and riding fakie (opposite end of the board forward). Once you master all these skills, this trick will be quite natural.
3. Ride outside of the wake on your heel side.
4. Approach the wake as if you're going to get air off it.
5. Wind up your body in the opposite direction of the way you are going to twist.
6. Unwind your body as you reach the wake and start your jump.
7. Bunny hop as you hit the wake, pull your knees up and turn 180 degrees by using the momentum of your spinning upper body to whip your legs around.
8. Allow your arms to remain taut and relaxed against the rope.
9. Land riding fakie, with your weight toward the back (the nose) of your board and on the toe side.
10. Ride outside the wake again and try to reverse the trick, jumping toe to heel.