As long as all participants are of sound mind, OVER EIGHTEEN AND NOT A DAY LESS, and agree to it, then go nuts. Do whatever the hell you want, as long as it harms no one else and does not result in permanent, physical injury.
And nothing involving animals. Because 1) THAT'S SICK and 2) Animals can't consent. They're not smart enough to consent. So using animals in any type of sexual act is wrong and horrible. I know there's this wierd as hell fetish involving eating insects and worms, and I guess that's okay because insects and worms are pretty much just biological machines and we kill them by the millions every year, but any animal above fish should NOT be used.
And of course, any pornography involving anyone under the age of 18 (or 16 depending on the country you live in) should be banned and ANYONE who watches or likes that sick stuff should be thrown under a semitruck. While on FIRE.