As has already been noted, most of the 'dirty little secret's listed so far are pretty... well, non-dirty. If I was ashamed of enjoying games like Viva Pinata or The Longest Journey I would presumably be filled with self-loathing, as they're great games. Hell, me and two flatmates all had our own gardens in VP (though I ended up hating the game due to the incredible glitches that afflicted it), and I tried to get as many people as I could to play TLJ.
The only game I can think of that I was ashamed of was Dead or Alive Xtreme Beach Volleyball, but I was always open about enjoying it (it's a compulsive game. Even when using both hands). That being said, I've had to stop myself buying the 360 sequel, on the basis of the many negative reviews of it. I fear that one day, however, I shall give in, and have a real reason to be ashamed.