Wow, thats never happened to me. Most of the people I know smoke weed. Everyone who knows me knows that I smoke. I don't have a whole lot of friends because I like it better that way. For one, people annoy me... and for two, I don't keep my smoking a secret from my friends. The less people who know the better though... so thats why I just have a small circle of friends. Now GROWING is a different story. Not even my BEST friends know about that.
As far as YOUR story goes though. I suppose that is bound to happen when you keep your smoking of weed a secret from friends. If they know (from the word GO) that you smoke, they'll have the option of just not being your friend... and you'd never have to worry about a situation like this. Or, just don't ever let the cat out of the bag.
You're pretty bold for breaking out a bag of illegal narcotics in the presence of an anti-marijuana type of person (friend or not).