There's only really one way to show your membership of the Cult of the Happy Doomer, and that is proudly and on your chest. These tees take all the hassle out of making one yourself!
It's important to remember the Happy part of the Doomer. Which is why this particular tee is available in a range of dark muted colours. Nothing too cheerful, of course, but maybe something to help co-ordinate with your existing wardrobe.