Something with an innocent-looking trigger, like the password with one character being a confusable, especially in most fonts. Such as a capital O where one actually expects it, whereas the real password has a zero in that spot. Or, if you memorize the Unicode methods for all three platforms, you use a Unicode confusable in the real password that looks like an ASCII character that someone would use in the trigger password.
That way, if you are “convinced” to hand over the password (https://xkcd.com/538/), you can write it out and let the other person trip the self-destruct on their own.
Back when jailbreaking iOS was really popular, there was even a jailbreak app that did exactly this to the entire phone - put in the wrong unlock code, and the phone rebooted and wiped itself. Great for people who worked against fascist governments.