Going back for a minute to foolish crewmembers, I should probably add a mention for Crewman Darnell from The Man Trap. While he didn't actually snack on a borgia plant as Nancy suggested, neither Kirk nor McCoy thought it too far fetched that he might have done. You'd think there would be some sort of Starfleet training about not sticking everything you find on an alien planet in your mouth, but apparently not!
Your comments made me think of those silica gel packs you find packed in the box with new electronic equipment. They're always emblazoned with the phrase 'do not eat'. I don't know about you, but I'd never be tempted to do that regardless of the warning. "Hey, cool, my new tv came with a snack!"