NationStates

The act isn't illegal by itself, but depending on context, it could fall under another crime.
Flag burning in support of an enemy nation? Sedition.
Flag burning in public, and not part of a registered protest? Disturbing the peace.
Burning a flag you don't own? Theft and destruction of property.
There are probably other situations where its illegal. Ultimately, you don't want to be the one arguing this with the police, so most people would avoid doing it.

Not illegal. People can burn any flag they want in protest.

No one would ever burn the flag of Luna Bean, but if someone did they would be forever shunned by society, because only a psychopath would burn a JPEG of a puppy

Legal, protected under 8th Amendment.

The act of flag burning is protected by the Freedom of Speech Act of 1922, and allows the burning of the National flag and various other flags without any penalty or risk of imprisonment.
However, in 1985, burning the National Flag is seen bad on a environmental stance, and if done it sends a strong message meaning "The problem is so big that the environment comes second at this point".

Not legal and not necessary in the first place since being caught burning the national flag pretty much alerts everyone in the nation that you're a coward or a liberal, with a execution squad arriving at your location faster than you could say 'run'.

Is is actually recommended, after keeping a flag for over a year (or if it gets ripped/dirty) it is recommended to burn it and buy a new one.

There is no law commending it or condemning it. Nobody really does it.

People in our nation are encouraged to burn our flag if protesting and to burn any foreign flags they wish. Flags, nationhood, and statism are against our community values as an Anarchist society.

President Ghejn once stated, "It's a citizen's right to express what they do and do not agree with, be it the government or their neighbor," so it's safe to say that flag burning is allowed in Ardenee.

Flag burning is legal in Arbaro.

Flag burning with the intent to desecrate is wholly legal in Emneshire and is a common method of showing dissatisfaction with the government in lieu of burning effigies of government officials (which also happens frequently).

We don't technically have a national flag, but we do still use the Tennessee state flag with the same manner of pride. The flag you see attached to our name with the black, yellow, and red lines is the flag we have adopted as our diplomatic flag, but we do not use it as the primary representation of our nation.

new law has been made: under new government there is no longer a law against flag burning

If on accident, no punishment
If it’s on purpose depending on the context, 10 dollar fine or no punishment.

They are asked why they’re not burning something more flammable, and might get weird stares.

Legal, but people will either beg you to stop burning the flag or ask you why are you burning the flag.

It is illegal and punishable by arrest or fines.

Illegal with the punishment being immediate execution

Illegal,The punishment would be 3 years in prison and a SV$500 (Sanvonic dollars) fine

Illegal,punishment would be a public flogging.

Not Illegal, allowed by the government completely.

legal.

Illegal depending on the flag, the current one is illegal to burn yet past flags are ok.

Burning the flag of Stratonesia is very, VERY CONSIDERED TO BE an "act of subversion towards the State"; due to the flag, alongside the coat of arms and the national anthem, being officially protected by law. Thus, whoever tries to burn the flag of Stratonesia shall be sentenced to a maximum of 5 years in prison.
Even if it's done on accident.
Burning flags of other nations? You can do that (but don't let their citizens of these nations catch you doing that).