Depending on context my favorite answers to 'Why do you need privacy if you have nothing to hide ?" are
“I need privacy, not because my actions are questionable, but because your judgements and intentions are.”,
“Arguing that you don’t care about privacy because you have nothing to hide is no different than saying you don’t care about free speech because you have nothing to say.” - Edward Snowden,
and “The only difference between a wizard hat and a dunce cap is the wide brim of privacy.”
ETA: None of which a fascist will give a shit about, but can be useful in politer society.
Depending on context my favorite answers to 'Why do you need privacy if you have nothing to hide ?" are
“I need privacy, not because my actions are questionable, but because your judgements and intentions are.”,
“Arguing that you don’t care about privacy because you have nothing to hide is no different than saying you don’t care about free speech because you have nothing to say.” - Edward Snowden,
and “The only difference between a wizard hat and a dunce cap is the wide brim of privacy.”
ETA: None of which a fascist will give a shit about, but can be useful in politer society.
My favorite is:
“So take off your pants. Right here, right now.”
Gets the point across quickly and viscerally.
What do you do if they drop trou?
Take a photo, and use that for face ID.
Or call the cops.
Inspect, very carefully, and point out every detail of course