I've always had told them I could read lips, but when they start talking, sometimes they don't move their lips too wide enough for me to read their lips....One time, I was sitting and waiting at the doctor's office, and this lady who came in and sat next to me while she also waited for the doctor, well she kept talking and talking, I couldn't tell her I was deaf because I was so shy so she kept on going and going, I just nodded and smiled, then she looked at me with a surprise look on her face and said " really ? " I was thinking 
what the heck did she asked me? what did I agree on?..... 
For now on, I always tell them I'm deaf up front in case I don't keep nodding on something that I have no clue what this person was talking about in the first place....sheeeesh!
