촐싹거리다 / 촐싹대다 (and sometimes just 촐싹이다) means going around acting frivolously.
It is the opposite of being composed and acting maturely.
Think of acting like small children, changing your mind frequently and not being able to stay in one place. It can also mean constantly coming up with new (silly / useless) ideas or trying to get such ideas into another person.
- 촐싹거리지 말고 여기 앉아 있어 = Just sit here rather than running around.
- 친구를 촐싹거려서 같이 돌아다닌다 = (He) entices his friend to go fooling around with him.