Whatever you do, don't peel the banana. Grab a narrow sewing needle that is as long as the banana is thick. Find a ridge and poke the needle into the banana, but not through the other side. Wiggle the needle around the banana inside the peel. The needle will easily slide through the banana and slice it. Pull out the needle and move a bit further down the ridge. Repeat. Each time you poke the banana and wiggle the needle, you are creating another slice. This does put marks on that side of the banana, but as long as you aren't pushing the needle through the other side of the banana, the other side will remain mark free. Hand the banana to a friend with the un-poked side up and have them peel it. They'll discover an already sliced banana!
Now that's cool!!! It's a great indoor activity, especially if you trick a friend while doing it!