5. a lot of people (especially older people I suspect) think "RSA" when they hear "public key cryptography".
I'm in my twenties and still have that reaction. I know elliptic curves exist, I even sort-of-kind-of have an awareness of how they work, but if I was asked to name one cryptosystem that used public and private keys, I'd definitely say RSA first and not elliptic curves.
This is likely in no small part due to CS education only really teaching the mechanics of RSA (modular arithmetic, Fermat's little theorem, etc), or at least, that still seems to be the case at Berkeley. I'd guess because elliptic curve crypto requires more advanced math to reason about (more advanced group theory, at least) and doesn't map as cleanly to existing concepts that non-math-major undergrads have.
cryptopals.com also doesn't cover any elliptive curve crypto until you get into the last set.
I would think that the (non-EC) Diffie-Hellman would also be easy enough to teach as well: exponentials and discrete log problem aren't any/much complicated than explaining factorization.
I'm in my twenties and still have that reaction. I know elliptic curves exist, I even sort-of-kind-of have an awareness of how they work, but if I was asked to name one cryptosystem that used public and private keys, I'd definitely say RSA first and not elliptic curves.