Some activities to consider:
-necrophilia (sex with corpses)
-zoophilia (sex with animals)
-pedophilia (sex with prepubescent children)
-hebephilia (sex with children beginning puberty)
-ephebophilia (sex with teenagers that have already gone through puberty)
-rape (non-consensual sex)
-extreme torture or murder associated with sex (that kind falls under rape...)
Some of these (mainly ones dealing with age) vary in legality, so assume that the activity is illegal where the person engaging in it lives.
I apologize if I got any terms wrong, I only double-checked with wikipedia.