because this is how he call men. in the chapter 13 he called Jeong-rok oppa and he called the blondie also oppa. you can read this in official translation.
Maybe because it turns him more on when he says “cute”
I mean “oppa”
That is what piss me off he calls any man oops
maybe in his way it's sth like daddy lol I don't know. for me it's fit to his sassy and flirting nature
If that's the case I am okay
Why is he calling him oppa instead of hyong it is getting on my nerves now