"Keep your goals away from the trolls."
I've only heard it in the past 15 years or so, so I didn't grow up with it, and I have no idea where I first heard it. It might be a regional thing, but I don't know.
(Wow. I just re-read this and I don't seem to know much of anything today, do I?)
Both of these are even better with "In bed" added to the end.