Contraband

If there's a way of making sure everyone knows you've bought stuff that you don't want to go around displaying in public - putting the thing into a black plastic bag is it
Theoretically it works wonderfully. The bag is opaque and black, no one would ever know what's in it. The catch is - everyone invariably does because that trick is about the oldest in the book.

Put something into a black plastic bag and suddenly you're as conspicuous as if you were walking around in yellow pants and a purple shirt with a board on your head that said "Look at me" in bold red letters.

I'm sure it started out as a sensible enough practice - but it's now become such a cliche that it has the exact opposite effect; instead of general public never getting to know there's almost a 100% change that they will, in fact, know exactly what's in the bag.

So the next time I go to buy a harmless bottle of wine as a housewarming present, I am going to carry my own bag. A transparent one at that.