Don't get me wrong: If you don't do drugs, I am not advocating that you start. I'm just saying that, if you are already setting out on a lucrative career of Laughing at Infomercials at Three in the Morning, please at least consider minoring in the promising field of Hallucinogenic Hilarity. Because if you're experimenting with narcotics now, odds are you're going to move on to something harder at some point -- if only to try it. And if it's a toss-up between stuff like coke and heroin or a bag of mushrooms, you grab that bag and run like you're a tiny Italian man in need of extra lives.
"A-ha! I can'a see through time'a!"
Here's a good rule of thumb: Do about half as much as your friends tell you to.
They will tell you to "eat the whole thing" of whatever they give you, regardless of the size of said "thing" or the strength of its contents. That's because stoners operate on a binary system of measurement: Something is either cashed or there's "a whole thing of it." If you're worried about your impending levels of inebriation, just take a little at first and squirrel some away for later. Also, if you can at all help it: Do not do hallucinogens in the city.