Wow, I love how a couple of dudes having fun with a great song and some nicely shot video can get people so worked up. First of all, that probably wasn't a joint--you could tell that by the way he rolled it and smoked it. And even if it was, who cares? We all have our poisons; for some it's a joint, for others it's fast food, and for others...there are a million of them. A joint is probably one of the least harmful things he could have been smoking out there.
Second of all, sure that's a great song--but they were having fun. It's supposed to be a joke, fellas. Ever heard of one of those? The fact that the original is such a serious, heavy song is what makes it funny. They're poking fun at the fact that dry fly fishing is taken so seriously by some.
Jesus. I think everyone needs to chill out, smoke a joint/drink a beer/eat a big mac, and then go fishing (with dries, of course).