Oh man, this is a tough one! If you tell people you stutter you elicit a certain response. If you keep it a secret then it could give wrong signals to people e.g "does this guy/gal have problems??". What has worked for me in the past is to explain causally. Using a certain experience. So if I'm talking with somebody at a conference I'll say something like "Man, there was a cute girl at reception there. Found it difficult to say hi because I stutter (rarely/sometimes/a lot). At least I found out where to go". It might make people curious but I'd recommend keeping it casual.