'Mucil' is not Indonesian word. I think it is from local language. But, I can understand the meaning of this word. It means like 'bandel' in Indonesian, or 'ngeyel' in Javanese. I don't know the exact equivalent word in English. But, I think it is more like 'stubborn'.
I agree with what Sosro said. Mucil isn't an Indonesian word. It's from a local language in Indonesia named "Banjar". The meaning is stubborn. Although, "bandel" in Indonesia, doesn't just mean stubborn, but also "naughty". Sometimes, mucil could mean "cerewet" (fussy, choosey).