talking about "Do Not Eat", we did that when i was in NS..
i was manning the medical store for the quarter and we had a
fridge in there for the stuff which needed to be
refridgerated..
so of course we'd put stuff like drinks in there.. and people
helped themselves to it even when it wasn't theirs..
so we "poisoned" it by putting in stuff like laxatives and this
horrific stuff called propantheline which was effing bitter...
we labelled the safe bottle as "safe for drinking" and the
spiked stuff as "do not drink"
the people almost always went for the "do not drink" bottle...
and we caused a lot of swearing 
Remind me of a piece of note I found stuck on the office pantry
fridge...
"Thou who eat my icecream will die a horrible death"
I found it extremely funny and took a pic, but i'm lazy to
upload...