What laws forbid this practice?

Paying desperate people to do demeaning things, self-harming, etc. For example drug addicted people will do almost anything for the cash to buy drugs; I can easily see some sadist paying them to debase themselves.

Against demeaning things, I doubt that there is much to prevent it, witness the porn industry. Against self harm, you would probably be in trouble with regard to OSHA regulations if nothing else.

Depending on their age or vulnerable condition, you could be tried for exploitation.

Come on, tell the truth, you’re planning to pitch a TV show aren’t you?

This case comes to mind:

I think in this case, because the specific sadistic thing involved fighting there were laws that applied:

The four defendants, Ryan McPherson, 19, Michael Slyman, 21, Zachary Bubeck, 25, and Daniel Tanner, 21, have entered not-guilty pleas to charges of conspiracy, illegally promoting a prizefight, and battery.

Paying the bums to commit a crime (even if upon one another willingly) is the first illegality. Engaging in an activity the government requires a license for without having said license is the next illegal activity.

I bet if one avoided those two rookie mistakes one could arrange all sort of “entertaining” activities for your desperate “independent contractors” (never employees; too much regulation there).

How is 2 bums agreeing to fight legally different from 2 prize fighters?

Not going to get into specifics, but both Boxing and MMA have promoted fights that would fit this.

Well, in Nevada (which hosts a lot of fights, since that’s where you find Las Vegas) there is a Nevada state athletic commission which regulates prize fights. Among their duties is ensuring that it’s a fair fight with adequate provisions made to ensure the relative safety of the participants.

New Jersey (home to Atlantic City) also has a State Athletic Commission to regulate fights. Again, there’s standards that have to be met before a fight can be sanctioned. You can’t just agree with your buddy to host a bout.

Some businesses, primarily very small ones, are exempt from some requirements.

https://pieinsurance.com/blog/safety/small-businesses-follow-osha/

Or at least you can’t do so for money; virtually anything for revenue comes under government scrutiny.

I seem to recall Homer Simpson being dressed as a giant Panda and put in the zoo for Mr. Burns’ entertainment. (It didn’t end well for Homer)
“I reek of Panda love”

There’s a plethora of laws, depending on the possible outcome - “reckless endangerment” comes to mind. If you are encouraging (paying) someone to do something that could result in serious injury, that could be one of the charges. Plus, IIRC conspiracy involves any two or more people acting together to commit a crime.

Even if it’s an amateur fight - most sports are arranged to avoid serious injury precisely because normal healthy people with normal healthy motivations want to avoid injury. So boxing includes soft(-ish) gloves and strictly enforced rules against certain injuries, observance of concussion protocols, etc. Deliberately avoiding these precautions risks endangerment charges.

A few years ago hockey was in the news, because North American hockey tends to include permitting fighting with older participants. However, if I recall what the outcome was for one such case or assault, the judge concluded while the participants bring a certain level of consent to a certain level of violence (ie. short fistfights) as well as the incidental rough and tumble of the game (much like football) - there are certain lines that they obviously do not consent to cross. Being beaten with a hockey stick, or blindsided with a punch from behind, or deliberate actions like being slammed into the boards from behind full speed, are not what the normal player expects from the game. These are specifically forbidden by the rules and understood by the players to be well outside the normal play and so could result in criminal charges.

I suppose the same reckless endangerment could apply to non-violence. Paying someone to walk a narrow ledge or eat potentially poisonous items, run across a freeway or practive knife or axe-throwing with a human target, or jump into a fast-moving river without a lifejacket or any rescue boats handy - all risk charges. Note that in game shows, there is always something like a lifeline or protective equipment. A company that could get sued for millions of dollars and has the ability to pay probably wants to avoid that hit to the bottom line.

Although there are laws against public indecency, simply degrading spectacles (like wearing Elton John plumage costumery in public or embarrassing signage) would not specifically be illegal.

People have gotten facial tattoos for money.

If we take violence out of the picture, there have been several TV shows based on the premise of paying people to do debasing or disgusting things on camera (the misnamed Fear Factor comes to mind, and I think there were several imitators). I don’t think I’ve heard of any legal action against those shows.

But one would assume that the participants signed various waivers in order to be on the show.

Paying someone to do something debasing or embarrassing would seem to be fine. Paying someone to do something illegal is obviously illegal. Paying someone to do something dangerous is probably reckless endangerment, and if they are injured or killed may be some form of assault or homicide. Paying someone to do something that could harm others is also endangerment.

But if we are sticking to just embarrassing actions, then unless it violates some nuisance laws you are probably OK. Or perhaps it could violate various sexual assault laws if it was debasing in a sexual way.