Purveyors of the delightfully cynical, Despair Inc, have created a wonderful drinking vessel that makes it absolutely clear when your glass is half empty.
If you feel The Pessimist’s Mug doesn’t quite get the message across, you can always try this Threadless t-shirt which illustrates the basic psychology behind the metaphor.
Personally, I’ve always preferred the approach from the anonymous quote “An optimist will tell you the glass is half-full; the pessimist, half-empty; and the engineer will tell you the glass is twice the size it needs to be”.
Link to Despair Inc Pessimist’s Mug (via Deric Bownds).
Link to Threadless Pessimist or Optimist t-shirt.
Mind Hacks 