When I used to smoke pot outside, then we had no glass pipes yet, so we used those metal ones. The nice thing about them, is there is no shotgun hole, and I have always found a shotgun hole pointless in small pipe, so we could cover up the bowl by cupping our hand around it, while flicking the lighter in one hand, while holding the small pipe in between our front teeth while inhaling.

What I'm saying is, if you smoke outside, you obviously carry around a small enough pipe to fit in your pocket, so just get a pipe that has no shotgun/carb hole, and cover the bowl with your hand.