Here are 2 techniques to avoid getting gunk under your nail and touching the fruit with your finger:
1. Hold the body of the banana with one hand and the handle with the other (right end of the picture above) and just snap it open. If the handle doesn't snap back easily, a possibility if the banana isn't ripe enough, then don't continue struggling with this method or you'll run the risk of squishing the top. Just move on to technique #2.
2. THE MONKEY METHOD. This is how monkeys peel bananas. If you're going to take advice from anyone about bananas then a monkey should naturally be your first choice. Just hold the banana with the handle pointing down towards the floor and just pinch the end that is pointing up (left end of the picture above) with your thumb and pointer finger. This will cause the end to split and you just go ahead and peel!
Now go practice and eat a banana!