If you truly have nothing to hide, I'm sure you'll have no issue whatsoever sharing with me your real name, address, phone number, email address, bank statements, all your bitcoin addresses, all your WhatsApp/Telegram/Signal/etc. conversations, your internet browsing history, and the login details for all your social media accounts. I just want to have a good look around and publicly post anything I find interesting. After all, you've got nothing to hide, right!?
This is just the best response to this argument. Whenever someone asserts that they have nothing to hide, I politely request permission to access their phone. Surprisingly, this approach even works with my relatives. The temporary awkwardness that ensues clearly illustrates my point that we all have things to hide.