Can you prove that I didn't just create everything and that you are not the only person that I allowed to exist, with everything around and your memories of everything just my doing, me "implanting" those memories and creating those people and places around you? C'mon, prove that I don't control your sensory input and your memories, that I don't control what you see, hear, feel, smell, taste and remember.
You cannot. Because the very instrument you have to prove or disprove that is the very same that I claim to control. Every time you say "but I can..:", my response would be "because I make it so" or "because I let you".
It is incredibly hard to prove or disprove something about your universe from within the universe. What you can argue with is what's more likely. What's more likely? That you're you, that your friends are your friends and that what you see, hear, taste, feel and smell is actually genuine and that your memories are what you really experienced, or that I put you in some sort of bizarre matrix world where everything you experience is just my imagination telling you how it should be?
Likewise, proving that God does not exist is not only moot (why bother?) but also kinda impossible. How do you disprove the existence of something that by its very definition has the ability to shield itself from any and all sensory input you might have? My reply could be that you should disprove the existence of the various other elusive and fun creatures from the flying spaghetti monster to the invisible pink unicorn, which is just as impossible.