By studying the opposite of what you want, you can identify important elements that aren't immediately obvious.
To work out what a terrible user experience for a web-based social network would be like, I brainstormed a load of nasty things that could happen. They fell into a few major categories:
1) It's just broken
Continuous fail whale or 404 errors, impossible to log in, posting just doesn't work, half the links are broken, there's a litany of bugs ...
Either build it for the wrong user (e.g. CEO instead of granny) or just don't think about the user's perspective at all. Bonus points for questioning none of our assumptions about the users. Why not design it to make it as easy as possible for the internal team to build and to hell with the users!
Whatever you do, don't you dare speak to or observe a single user! #terrible-ux
3) Make it unfocused, with feature creep
It should definitely cater to every whim the coders and designers think of as they go along. People definitely want a one-stop shop where they can do everything slightly badly. And the users who shout and moan the loudest should get all the features they demand.
4) Be unexpected and inconsistent
Definitely use mystery-meat navigation.
And always give the user a surprise by making stuff they could never expect happen.
5) Be unclear
Make buttons look like text and text look like links and buttons. Don't include anything that tells the user where they are or what they can do next. Make any instructions cryptic – it's more fun when the user has to solve it like a puzzle!
6) Make catastrophic events trivially easy
7) Make the core useful things nearly impossible to do
Users appreciate the result more if they have to work for it. There should definitely be some unnecessary steps in every process. And make sure it forgets or garbles all your input if you do something even slightly in the wrong order.
Inspired by this article on James Clear's blog: http://jamesclear.com/inversion
What else can you think of?
Please add your ideas for how to make a terrible UX in the comments... Prize for the worst.