A reference to a series of Saturday Night Live (SNL) skits by comedian Chris Farley in which he plays an overweight, out of work, motivational speaker who lives in a van down by the river. He is routinely hired by concerned parents to speak to their children about the dangers of gangs or drugs. In response, he overstays his welcome, trashes the house with his physical, slapstick humor and scares the kids by using his life as an example of what not to do.
"If you do drugs, you'll end up like me... living in a VAN, DOWN BY THE RIVER!"
its much funnier when he says it, trust me.