Back in the late 80s/early 90s there was this anti-drug PSA that used to air while cartoons were on when I was like four and five years old and it scared the living crap out of me. It consisted of some dealer gradually transforming into a snake monster creature as he was directly addressing the audience. I had nightmares about it, and I remember him sticking his snakey tongue out at you at the end. I would assume I dreamed it up if not for the fact that I so vividly recall how much it freaked me out as a kid.

EDIT: Nope, I didn't dream it up. Thanks YouTube.