I thought to myself, "Hey, let's make gifs for every single time a Winchester says 'Dude'."
And then, "Hang on, I'm not that insane yet. I'll do one per episode, and work my way backward."
It should surprise no one that the last time either Sam or Dean said "Dude" was in 8x08 "Hunteri Heroici".
(
Under a cut because not everyone likes gifs )