Oppa

Oppa (오빠), a korean word, means older brother, and can be used for several things;

For a girl to call an older male, to imply she trusts them.
For a girl to call an older male, to show respect.
For a girl to call an older male, in a flirtatious way.

This word's meaning can often be mistaken by daddy instead of older brother. Although it can be used in a flirtatious way, it isn't a way to call someone "daddy".

Also is what many ARMYs call the members of the k-pop band, BTS. I'm assuming in a flirtatious way.
The member Jungkook (the youngest) has a great dislike for being called oppa.

Example 1:

Girl: Hey, oppa! Wanna hang out today?
Boy: Oh, sure.

Example 2:

Girl: Hey there, oppa~
Boy: *Flustered* ..oh, hi.

Bonus example:

Fan: JUNGKOOKIE OPPA!
Jungkook: *TRIGGERED* I A M N O T Y O U R O P P A

by smolbeanjungkook June 29, 2018