This started when the hippies found that pot keeps you from having a hangover the next morning.
"Lit" people are usually too drunk to be mellow and too bombed to hurt others, this results in them bleeding themselves.
Me: puff, puff, pass
lit idiot: "watch me break this door with my head"
Me: "I'll call the ambulance in advance so you won't have to wait so long"
<lit idiot breaks head with door>