면서 그러다

saying that while doing it

-(으)면서 says two things happen at once, and 그러다 stands in for "say or act that way" without spelling it out: 노래 부르면서 그러는 거 전혀 눈치 못 챘는데, 기 빨린다, 좀 이러면서 그러고, 나를 잡아주길 바라면서 그럴 수 있는데. It very often follows a quoted line ending in 이러면서, where the quote carries the words and 그러다 points back at the behaviour: '왜 너 스스로...' 이러면서 그러는데. The vagueness is the point — the speaker is gesturing at conduct they would rather not describe.

Register: casual, vague by design