Ree-you (grand champion) - The most common mispronounciation. I will still say “yeah?”
Rye - Like the bread.
Rye-you - The second most common mispronounciation. Still will respond to it.
Ray-you - Occasionally this is said.
Are-you - I am. I am Ryu. This was pronounced over the intercom in middle school.
Ryan - Sometimes they just act like they read it wrong I think. Sometimes they actually read it wrong too.
garoo - I think this person misheard when I said, “It’s Ryu, like kangaroo”
Gru - My little sister called me this for almost 2 years. Like the minions movie guy.

I have come up with the most non-ambiguous, clearly said, hard-to-mishear name of all time: three. If you cannot get my name right, just call me Three, like the number.
I refuse to believe that you can mishear Three. It is just way too hard to not hear the number Three. Plus, who else would be named Three? I would always know you are talking to me.