I say things I can't prove all the time. At least, things I can't prove to any of you. For instance, I'm a first degree black belt in shaolin kempo, I can't prove that to you. I could take a picture of the belt, but I could have just bought it online. I could take a picture of the certificate, but I could have forged that. I could take a video of one of my old senseis acknowledging my rank, but then I have to prove A: he is who he says he is, B: he's not lying to you for money, or C: I didn't trick him somehow. I'm sure for each attempt at one of those, I'd have something else to prove it's valid.
Luckily, I don't care if I can prove it or not. It's your choice to make a judgment call on if you believe me. If you do, great. If not, I can try to convince you, or ignore you. No cursing you out needed.