I avoid anything that hints on incest, for instance, even if it's only fantasy. I also avoid threads where I feel one's fishing for underage content, like "when did you first..." kind of threads. These are the threads that make me feel like blocking people. I also avoid music, squirting, drugs/alcohol and games threads, though I do take a look at those now and then, if the site is really quiet everywhere else. What do you avoid?