Is there a law in the USA which punishes people who out "closeted" homosexuals?

Nope. As long as the person revealing this is telling the truth, he cannot be charged with libel or slander if he has evidence to that effect.

Politicians who sleep around can tell you all about it. Also, the New York Post loves to "out" people all the time for various things, including the sexual preferences of public officials. As long as the facts are verifiable, then there is no legal recourse. Even if the person was fired from his job and assaulted by somebody because of it, he could only go after his employer for discrimination and after the thugs for hate crimes.

It's called the freedom of speech.

Nope, the only way it would be against the law whether it be criminal or civil is if it wasn't true and that person had some sort of monetary loss as result of it. If its true, there is no recourse in the courts.

Not sure about American law, but dont think it would be that different to the UK, to be honest

He would definitely have civil recourse should what you do cause him financial damage. (This could include loss of earning should his health suffer as a result etc)

It could possibly be criminal if you out him in any way is classed as inciting hatred.

If he can prove that your accusation caused him any monetary damages or maybe that it caused you to lose a friend or something then he might be able to sue you in civil court for either defamation or harassment, but probably not since it's entirely true. Either way, you shouldn't do that, it's frickin mean.

I think so because who on planet earth would like to be called a homosexual, exsecially in USA ?

It is not technically against the law, but he would have a strong case against you, if he were to sue you.

No.

But in my opinion it is really ****** up.