The word cabrón refers to a cuckold, a man whose wife or girlfriend has been unfaithful without his knowing about it. Although the word also means ‘male goat’ and is inoffensive in that context, when used in slang, it can be extremely insulting or offensive. The word also has several other meaning in current slang.
Although the idea of being cheated on by a woman is uncomfortable for men around the world, it is particularly unpleasant in Latin culture, so the word cabrón should be used with caution, and only when you are very comfortable and confident with it. The Real Academia Española gives the following definitions for this word.
1. adj. coloq. Dicho de una persona, de un animal o de una cosa: Que hace malas pasadas o resulta molesto.
2. adj. vulg. Se dice del hombre al que su mujer es infiel, y en especial si lo consiente.
3. adj. coloq. Cuba. Disgustado, de mal humor.
4. adj. coloq. Cuba Dicho de un hombre: Experimentado y astuto.
5. adj. Méx. Dicho de una persona: De mal carácter.
6. m. Macho de la cabra.
7. m. Hombre que aguanta cobardemente los agravios o impertinencias de que es objeto.
8. m. Am. Mer. Rufián que trafica con prostitutas.
In other words, cabrón can refer to something that is annoying, a man whose wife or partner has been unfaithful, a way of describing someone who is experienced, or someone with a bad personality, a man who is a coward and tolerates all manner of annoyances, or a pimp.
As an interjection, ‘carbón’ means something like bastard or asshole.
• ¡Cabrón! (You bastard! You asshole! You stupid ass!)
Calling someone a ‘cabrón’ is to say that the person is a bastard, asshole, or jerk. This can be used directly or indirectly in speech.
• Eres un cabrón. (You are a bastard/ass/asshole.)
• El muy cabrón me robó el carro. (The bastard stole my car.)
The word ‘cabrón’ is used widely in the Spanish-speaking world, though its exact connotation and degree of offensive varies not only with the region but also with the people using it. Teenagers in particular tend to use slang openly and without reservation. Non-native speakers are best off not emulating them.
As with all curses, be very careful when using any form of cabrón. Even native speakers can cause offense, so non-natives are usually better off just avoiding them. But ‘cabrón’ and its accompanying idioms are so common that you have to know them.