A bit of arts and crafts deftness that results in a banana which is already sliced into segments before it has been peeled. Present the banana to a nephew, a babysittee, a person you're trying to woo, and enjoy their bafflement when they peel it to find a neatly sliced banana inside. I learned this from watching Mr. Wizard when I was eight, but it has served me well in my adult life. It stumped a grown-up child prodigy/pothead, so it just might impress the cynics in your social circle.
You will need:
1. Thread the needle. You don't need to double the thread, but make sure there is enough excess length that you don't lose the thread in the midst of a "stitch."
2. Choose a starting point on the banana. This is where you'll be making your first "stitch." Start at one of the "corners" that run up and down the peel, not in the smooth middle panels. It's best to use a banana that is a bit ripe and has a few brown speckles, because they help to camouflage the entry and exit points from the needle. You can slice the banana into as many or as few pieces as you have the patience for. I usually just make three or four pieces...enough to show that I can repeat the trick.
3. Slide the needle horizontally under the peel from one corner to the next, leaving plenty of excess thread hanging from the entry point. Be careful to avoid putting the needle through the fruit itself. You want to keep the thread between the peel and the fruit. Don't skip corners (i.e. slide in one corner, and slide out two corners away). If you skip corners, the slices won't be as neat. It will also be easier for someone to figure out how you did it. You can slide the needle through at an angle if you want (resulting in a banana cut on the bias) but this requires follow-through that demonstrates an understanding of geometry. Have at it.
4. Once you have pulled the needle back out at a corner, re-insert it into the same point and repeat step 3, moving on to the next panel. Keep your needle steady so that it makes the smallest holes possible, and again try to use the natural brown flecks as nifty cover-up for your needle work.
5. After you have threaded all the panels (usually five), bring the needle back out through your original entry point. Now, the thread should be completely wrapped around the circumference of the banana, just under the peel, with both ends of the thread sticking out of one small hole in the peel.
6. Carefully grasp both ends of the thread and pull straight away from the banana, firmly. The thread should easily cut through the banana and slide out of the hole in the peel.
7. Repeat as much as you'd like on the rest of the banana in order to best impress someone (no "most impressive banana" jokes, please).
Though I've broken this down into meticulous steps, it's really quite simple and quick. You can experiment with making V-shaped or zigzag slices, too. After you're finished with your banana, smooth down the needle marks and make sure it doesn't look too manhandled (no "manhandling your banana" jokes, please). I've had people inspect the peel and still not notice the small marks that this trick leaves. Mostly, people just end up thinking I'm pretty cool and a little dorky. Which is just what I want them to believe.