We had a wonderfully educational discussion some time ago about this. I was curious about those insults we hear all the time in k-dramas.
개새끼 gaesaekki (pronounced kaesaekki)Everybody, including gangsters and people who really really despise and hate each other, seemed to use kae-saekki (-ya) as the harshest insult in the world. So I dug more only to find out that it literally means. ʺSon of a dogʺ Derived from 개[gae] meaning ‘dog’ and 새끼.(= baby). And that "saekki" is indeed used lovingly by mothers for their babies!
미친새끼 mi-chin-sae-ki (usually translated as crazy bastard, crazy asshole). Literally "crazy baby". Does not mean literallly bastard, as in "illegitimate child". It's just a generic insult.
미친년 mi-chin-nyeon Crazy girl/crazy bitch /crazy wentch. "Combination of the verb미치다[michida] ‘to be crazy’ and 년[nyon], pejorative slang for 'girl' (but not necessarily of loose morals)
Try to sub in context. "
기지배/기집애/ gi-ji-bae (prn. kicchi bae) usually translated as "you girl" or "wench"
It is almost a synonym of 'girl'. It does not mean bitch or who*e! It's not considered as a nice word, and people don't like being called that, but it's not taken as an insult. Much more common among not-so-well-mannered or uneducated people. You can use this word toward people you are very familiar with: usually between girls who are close friends (from kids to middle age), or a mother to her daughter. You use this word when you don't like what your close friend or daughter does. When scolding or blaming, but sometimes in a friendly, joking way.
So all these are really milder than the translations. What is really offensive are all the Korean insults which start from "shib...", which involve intercourse and such.
I usually avoid swear words in dramas. I don't like either hearing them nor reading them. And reading is not the same as hearing, it is much more impactful than hearing. If you hear it, it immediately goes away, but the subtitle will stay on for your eyes to "enjoy" and sink in for a few seconds more.
I find asterisks ridiculous: saying without saying, it's hypocritical and coy and ... just bleah! You might as well write the whole thing! If we really want to substitute, frankly I prefer to do it like in comic books, #$%^!!@*&%! Because this implies "the worst insults you can imagine", and it's fun!
I have gone to great lengths to make lists of alternatives to the usual 2-3 insults people use in real life, which are used so often and so freely that they have totally lost their meaning.
However, I give free rain to translators in films. For instance there was a film, "Fasten your seatbelts", where one character curses all the time, very heavily. And another one, "Sunny" (one of the most wonderful films I've watched here, I warmly recommend it) where one of the girls was known as the Queen of Swear Words and she was so inventive! Of course you cannot censor these, the film would lose all impact.