If you want to see the back of your head go near a black hole. Black holes have a region around them called the photon sphere. This is a region where light can wrap around many times around the black hole coming pretty close to its original position before either spiraling out very far away from the black hole or falling into it. So if you look straight ahead and you will see light that headed backwards and came around to the front of your face, that's what we're talking about. That would make for a weird picnicYou know do you know who you're looking at who you see right in the back of them at the same time and then you walk towards them but you don't