How to deal with flight attendants behaving unlawfully?

To be honest and as a cabin crew member, I have never heard of such a thing. The second advantage of being a flight attendant is meeting different people from different countries and cultures (after going to many places). So having a racist flight attendant is like having a doctor that does not like to touch people! or a nurse that can not see blood. So if there is a racist flight attendant, then she/he must be one of a kind, not something you might see in every flight, not even once in a life time.

Regarding ignoring requests, this is surely not because of racism, this is totally the company's mistake. If a company is enforcing its onboard services, you will never see such a thing. So if this behavior was found in one attendant, be sure it is a company wide issue not a racism issue.

Regarding spitting on food, come on! Again, I do not think this happens. If it really happens, then I guess the rule of "Don't Piss Off People That Handle Your Food" can apply here. Again, from an insider, I never heard any flight attendant ever mentioning this idea, even as a joke.

Regarding fist fight, it is bad by all means (unless it is an act of self defense of course). Flight attendants know how to handle passengers, it is very rare (out of the millions of flights each year) when a flight attendant picks up a fight with a passenger, usually it is started by the passenger. Just avoid such a case, the crew will be filling forms and calling security to be waiting upon arrival, and they know how to deal with these situations, it is almost never a win situation for the passenger. In general, getting physical is a bad idea.

Finally, If you really felt that a certain flight attendant is ignoring a certain ethnic group while serving others, act correctly. Start by requesting to talk to the cabin in charge (purser), explain to him/her what you have experiences. A one or two witnesses to backup your claims and there will be a quick action on the spot! If this did not work then try escalating things and write an official complaint to the company (or sue the company if you have enough proof). Any airlines will not want such a reputation and will try to compensate you so things do not go out of control (media, etc.)

I'd say it's fairly straightforward, you deal with them on a plane just like any racist individual you meet on the ground.

You have several options:

1. Explain to them that you feel they're being offensive in their words/behaviour. They may not realise that certain words are bad, and that may solve the problem on the spot.
2. Ask another flight attendant if you can get service from them instead, as the other flight attendant (note their name) is making you feel uncomfortable. @MeNoTalk may be able to tell you if this is common or not, but I'd assume it's possible.
3. Note the flight attendant's name. If they won't give you their full name, ask another attendant - you could always tell a white lie and say you want to give them a good note to their airline. When on the ground, write an email to the airline, indicating the flight number, attendant's name, description, and the time and details of what they said and did. If other passengers witnessed the incident, ask them if they'd mind sharing their contact details to act as witnesses.
4. Finally, if you don't get a helpful reaction from the airline, you could go to the press. This is an extreme option, but articles like this tend to spread pretty darn fast, and are very effective at getting a reaction/apology from the airline.
5. If they've done something criminal to you on board, you can go to the police. Obviously this would have to be pretty serious. For this one you would ideally want witnesses' details, as this will strengthen your case.

Odds are incidents on a plane would be rare, I'd think, as they have training on cultural differences, and how to handle passengers politely and well. However, there's always the potential for someone to say something stupid.