I just saw a video where they were talking about the word "oppa"..i don't think i could ever call someone oppa because Opa is the german word for grandpa.. it's always weird to hear/read it..
oppa one suggestion pls would you like to give us a lesson about the korean words or sentences we should not use in daily life and while meeting olders people thnx in advance ps: not now of course i know you're busy when you have time pls do this