The words every fan uses

최애 is Sino-Korean: 최 'most', the same syllable as in 최고 'the best', and 애 'love'. Swap 최 for 차 'next' and you get 차애, the runner-up. Two Sino-Korean syllables can make a new word as easily as English makes one from Latin roots, which is why fandom slang so often comes in pairs of syllables. 컴백 and 팬덤 went the other way, borrowed from English and then given a Korean meaning. 'Comeback' in Korean means a release, not a return, and English-speaking fans have taken it back with that meaning, which is why it puzzles everyone else.

덕 comes from 오덕후, a Korean respelling of the Japanese otaku, 'obsessive fan'. It shrank to 덕후 (deoku) and then to 덕, which now combines with Sino-Korean syllables as if it were one itself: 입 'enter', as in 입구 'entrance', and 탈 'leave', as in 탈출 'escape'. 질 is a native suffix for an activity you do over and over, as in 걸레질 'mopping', and it often carries mild disapproval, as in 도둑질 'stealing'. So 덕질 is knowing and a little self-mocking. The set treats a fandom as a place: you enter it, you live in it, and one day you might leave.

None of the fan words is rude. The risk is a different one: they mark you as someone inside a particular world, and used with someone outside it they sound like jargon, or like a joke at your own expense. 최애 and 컴백 have spread far enough that most younger Koreans know them whether or not they follow a group. 입덕 and especially 덕질 are still fandom words, which an older person may recognise but would not use. Choosing a column is the same judgement as choosing between 'my bias' and 'my favourite' in English.