I'd just let the guy heckling sit there and I wouldn't say anything. If someone feels the need to act foolish and say something like that then they're more than likely jealous. So take it as a complement. My entire last semester at school I worked with two guys that constantly called me "steroids". They didn't know anything but just were upset by the fact that they were my height just 40lbs lighter
And it might have had something to do with the fact that one of them's ex gf *who is an extremely hot redhead, talked/talks to me all the time. What the hell ever, people are going to say what they will, but it doesn't matter just keep lifting.
I'm not against steroids (obviously) I'm just against people using them irresponsibly, which I used to see a lot in college. And that's the only reason I would ever call someone out myself.
I was also called out by an ex gf months after we broke up a few years ago (While on my first cycle of EPI). She looks at me and says "Are you on something you look bigger" and then proceeded to try to hook up later that night. I just told her she'd never know and I'm more interested in girls that keep themselves up now. It pissed her off but whatever, she deserved it for constantly badgering me about creatine being a steroid.