Nice shirt. Well, this is pretty normal. The foreign language is just a group of sounds to you, so you just make the sounds without having a feeling of the meaning. Don't worry; it's happened to me as well. Also, I'm pretty sure that when you say these bad/sexy/insulting words it sounds robotic and "copied", so the listener knows you don't fully understand. So, consider it a goal to feel the words! :D

I take a wild guess: You hear them all the time in movies and TV series. Specially HBO productions. That makes them sound normal. And some people really talk like that. But I think when you don't have a clear understanding of the meaning and when to use them I strongly suggest not to use them at all.