Talking To Yourself
noun
独り is when you're alone. 言 is when you say something. So, when you say something and you're alone, you're just talking to yourself.
ひとりごと
The reading for 独り is just the reading for 独り. The reading for 言 is an exception, though. It's ごと, which comes from こと. Just think that as you're talking to yourself you're telling yourself over and over to go to hell. You're mean to yourself, and you're also insane, which is why you keep saying that out loud to nobody but you.
君が女性に対して口がうまいのは知ってたけど、その練習のためにそんな風にブツブツ独り言を言ってるなんてこれっぽっちも知らなかったよ。
I knew you were super smooth with the ladies, but I had no idea that you practice talking to them by talking to yourself like that.