I've been alone a lot lately, and in my lack of human contact I've taken to muttering things like "I WANT TO KILL" and "******************." Luckily I don't think anyone has heard me.
Lol! I've been like that too, but I think I have been heard several times.
Recently, I was out walking the dog and muttering to myself (not realising I was doing so) and someone passed by on their bike and looked back at me like I was a freak D-: