Is it normal that i mutter to myself angrily and don't notice?

It has come to my attention that when I get deeply involved in a day dream, usually including some form of violent justice or something, I make weird grimacing faces and mutter in sharp harsh undertones. I didn't notice really until my sister started looking at me funny when I was pacing around the house doing it...lately I haven't felt like doing it as much but sometimes I still get pissed and end up muttering stuff like "motherfucker", and "fucking kill you bitch" at weird moments even when parents, relatives, or friends are around.