I love surprising people like that. Whenever I play "guess my age" with people, they guess anything from 19-26 when I'm actually 34. In addition, nobody EVER believes that I used to weigh 240 lbs. I'm about 160 now. I also like how nobody expects that I enjoy punk and metal music and that I play in a heavy band. By the same token, people I meet at shows are surprised that my day job is a special ed instructional aide.
I remember one time playing old band's EP release show a year ago, some dude asked if I wanted a beer and I declined because I didn't drink. Then he asked me to join him for a smoke, and I declined because I don't smoke. Then he asked why I was at a punk show and I mentioned that I'm playing in the next band. After we played, he grabbed me by the shoulders and exclaimed, "Why didn't you tell me you could shred on bass like that?!?!? You're the f'n TRUTH man!" And I politely said, "That's exactly why. I'm just full of surprises." I made sure he got a CD, a link to our Facebook so he could come to more shows, etc.
And when the band I currently play with played a show on Saturday that my old crowd attended, none of them expected what they saw. I love defying people's expectations, particularly when they underestimate me.