I either just ignore them, or tell them "they're just jealous" which I think is true most of the time.
I know this other guy at my school who can solve it, but it takes him like 10mins. Whenever I start cubing and he's around he calls me a showoff. But whenever I see him solving it, it's always in front of people, never by himself.
I usually don't cube much in public anyway, but I sometimes cube at school when I'm bored. I try not too pull it out too much though, because its really annoying when people ask to play with it. I used to let people play around with it all the time, until my stickers started peeling off quickly, every time I gave it to someone they would be turning really slow and still pop it, and people dropped it as well. Now I never let anyone touch my cube except close friends.
Its too embarrassing in public when people start staring at you...