Depends on how familiar I am with them.
Most people who know me, won't say it, though, it's usually random people.
I had someone say this to me about two weeks ago when she was gabbing away. She stopped to ask me why I was being so quiet. I thought to myself that even if I wanted to say something, I couldn't, so why even try? I just told her I didn't feel like talking, so she responded with, 'You're always this quiet, I bet.' Not sure what that meant...
If she knew me, and I actually liked her in some way, I wouldn't have been so quiet.