My foreign friend's favorite word was pedophile (sp?). He thought it sounded so neat and he would just blurt it out whenever he could. Everytime he did that, everyone would just look at him funny. We would tell him to stop saying it, because he would say it and he didn't even know what the word meant.
My favorite word is actually "great". Everytime I laugh at something, I always go "That was great". I would even say it when something wasn't great. One time, my friend was telling me that someone died from constipation and I started laughing and I said "That was great", even though it really wasn't.