in which he secretly dances to girl group songs because he's good.
a girl catches a guy (who's known as the "cool" and "badass" or whatever guy at school) doing ridiculous kpop girl group dances (like Pick Me by Produce 101 or Cheer Up by Twice, not that their dances are ridiculous but he makes them ridiculous) and singing/humming along while cleaning the school's storage room as a punishment (because he did something but the teacher realises that he's too immune to detentions). The reason that he does girl group dances then might be because his little sister/brother put the songs on the night before and he can't get them out of his head.
