"I know you are, but what am I" was a poor response back in 2nd grade, too.
Also, it seems that your issue is much more with the stereotype of pot head, rather than the reality of many of the people who smoke. The last times that I smoked, I was either a) climbing a mountain, b) walking around a park, c) discovering a new city or d) at a shitton of clubs and bars for halloween.
But no, we can pretend that I was just sitting around listening to music and eating


