Vernon doesn't look like the type of guy who has ever smoked a joint in his life.
As for cigarettes, I imagine schools probably smelled more like cigarettes than they do today. Teachers smoked, kids smoked....everyone smoked and even if you didn't, that smell was on your clothes, on your things.
We live in a smoke free world today.
Did you also notice the enormous amount of weed Bender had on him?? Like...anyone would ever have that amount of weed on them at any given time.
I agree that the characters stopped giving a sht at that point.
This is a John Hughes film. It's a running theme in his movies for adults to be portrayed as clueless idiots. So, it's possible Vernon wouldn't have caught on.