UI HATERATION:
Windows ME
Windows Vista (which I have only looked at/heard reports second hand)
ANY entirely Flash-based website (like most "upcoming" movie web sites).
The CSI: 3 Dimensions of Murder video game. I picked up this video game on a whim, being a CSI fan, and wanting to see what the game would be like. The game consists of going to crime scenes, clicking around until you find all the evidence, going back to CSI and clicking on all the various rooms and equipment until you have processed all the evidence, and talking to all the various characters suspects until the crime is solved (and yep, "talking to people" consists of pressing the space bar until all the dialog has been displayed -- you frequently get options of questions to ask, but you have to go through them all to "solve" the crime anyway, so that doesn't really matter).
It is a video game that plays itself. It only requires input from a human(?*) to make mouse clicks in the right places and space bar through the dialog. Add to the fact that the "3 Dimensions" of the title refers to both the number of cases you have to solve in the game (three, yep, only three) and the fact that all the characters (voiced by the actual CSI actors) are given half-assed 3-D computer animation, so you've got a major Uncanny Valley thing going on all game, and this is one of my top contenders for Worst Video Game Evar.
(*Not only do I think a chimp could play and "win" this game as fast as any human, I think a chimp could write a script to randomly send mouse movements, clicks, and space bar hits to the game, thereby removing the need for any living thing to be involved in "playing" the game.)