For those that haven't seen the UK TV show: Select just three things that the world (or just you) would be better off without. Dump them into Room 101 and they will be eradicated. Your readers must then try to persuade you that you're being unreasonable and that there might be unforeseen consequences if your choices were allowed.
If you do this meme - increment the letter in the title so that 'Room 101-a' becomes 'Room 101-b', and so on. Copy and paste the above text into your own journal.
Spammers. Producers of not just unsolicited junk email, but junk paper mail, off-topic posts in LJ communities and Usenet, junk comments, all that sort of thing. If I start to write about this there's a distinct danger that the heat-death of the universe will occur before I finish, so I won't start.
Chauvinism of all kinds, particularly homophobia and skewed attitudes to other non-majority lifestyles. I and my friends have more trouble from people who are down on bisexuals or BDSMers or people with tattoos or piercings or who are science fiction fans or goths or whatever than we do from a lot of other candidates for Room 101.
Religion. No, stick with me on this. I've written elsewhere about the distinctions between religion and faith -- and while I believe that faith is a valuable thing, a helpful thing, something that can make a difference in a good way, I believe that religion can be deeply divisive, deeply destructive, something that can make a difference in the worst way possible. Religion, when it involves turning some pseudorandom individual's faith into a set of rules, lifting those rules out of context, and then applying those rules blindly in circumstances in which they make no sense at all, belongs in Room 101. With a lock on the door.
I'll concede that the second and third items may have something to do with each other. I may have been influenced by a couple of things I've read recently.