I firmly believe being personable and professional will prevail.  It will project your confidence and give the aura of commanding yourself so that others need to think strongly before trying to cause a scene.  As previously stated, anyone who tries to call a person out for past employment, regardless of how embarrassing, is also calling themselves out as well as showing their lack of professionalism.  

I would also feel that rehearsing a few comments in the event of this happening would increase your confidence. "Hello, I thought you looked familiar.  I am currently developing/ maturing my company and I would like the opportunity to discuss it further if you are genuinely interested."  It acknowledges their comment, but also dismisses it and their behavior to regain control of the situation.