1. What does it mean?
뻘쭘하다 describes the uncomfortable pause when you do not quite know where to put yourself: a greeting goes unanswered, a joke falls flat, or you realize you have arrived in the wrong place.
Also written or said as 뻘쭘, ppeoljjumhada
2. The nuance
It is about social discomfort rather than fear. 뻘쭘했어 looks back at the feeling, while 뻘쭘하게 can describe doing something in an awkward way.
3. Examples
“다른 모임인 줄 모르고 손 흔들었다가 뻘쭘했어.”
I waved before realizing it was a different group, and felt awkward.
“농담 뒤에 아무도 안 웃어서 좀 뻘쭘하더라.”
Nobody laughed after the joke, so it got a little awkward.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.