I definitely don't store my SSH keys on stranger computers. I however used passwords on my relatives or customers devices on numerous occasions. Don't pretend you never did, I'm not going to believe you.

Sure, I've used other machines in the past. I prefer not to though in most circumstances and assume that any account / password that I use on said machine is compromised from then on.

This was something I changed when I realized that a tax related government agency's machine I was using about 10 years ago man in the middled SSL connections to my online banking. Who knows what was logged and what the retention on that was? I don't have time or the inclination to ensure every relative's / customer's devices are secure, so I use my own or go without.