Rule #1: Never ever ever call him "oppa" before you're ready.
After we had been consistently talking and meeting for 3 weeks, I slipped up and typed "Oppa, fighting". Without thinking, I sent it and his reaction speaks volumes (see screenshot).
"Oppa" can have some negative aspects to it. It has a range of meanings from being responsible, protective, to having more power, status, and right. Once you say it, you can't take it back. Oppa loves~~ to be called oppa and even talks about himself in the 3rd person, just to try and make me say oppa more too.
Him: "Oppa loves you" Me: -smh-
Stereotype That He Meets 100%: He likes to match.
Thankfully there have been no matching outfits yet, but if we accidentally wear the same color, he'll make sure to mention it ("Couple color~"). Also, he matches my steps when we walk (sometimes on accident), but if I really want to tease him, I'll double step and he'll struggle to catch back up.