I think I have this a bit, every once in a while I just get this urge to instantly repeat something I just heard, usually it's someone's message ringtone, but sometimes it's a few words or something like that. It's not about the words though, it's the sound, so it's usually when someone says something funny sounding, or something in another language, or something said with an accent.
I've had a few embarrassing instances of this though, so I control it now and hardly ever repeat things people say, except quietly under my breath. Although it's getting kind of hard recently, since where I work about half the people, including my boss, are Arabs, and to me for some reason there's nothing funnier than an Arab accent in Hebrew (today my boss told me to "sbray and bolish the counter", Arabs don't have the sound "P" in their language, for some reason this provides me with endless humour).