oh lordie..i think they all do it. have you ever seen that show "the middle" with the little kid that whispers to himself? my son does that! he will hear something on tv, or i will say something, and i will hear him whisper it to himself...then later he will use it. it's like he's trying it out. my mom thinks it's hysterical....*sigh*...
also, one time in a fit of frustration, i said, "oh i HATE the rain!!" now i am a mom that doesn't like to hear my four year old say "hate" about ANYthing, so when he repeated it, i told him, "well honey, it's not a very nice thing for us to say - we shouldn't hate the rain because god sends it to water the flowers and the grass and the trees..." i gave him the whole spiel. so now when he comes up with something, he'll ask, "mom, is it okay to hate X?" mostly the only one we've come up with that it was okay, was Darth Vader. but then he saw the last (old) star wars movie where we find out he's Luke's dad, so my clever son has figured out that you can't really hate Darth Vader either. he was a little bit nice...
sorry, got a little off topic lol...