A man is smoking a cigarette...

A man is smoking a cigarette and blowing smoke rings into the air. His girlfriend becomes irritated with the smoke and says, “Can’t you see the warning on the cigarette pack? Smoking is hazardous to your health!”To which the man replies, “I am a programmer. We don’t worry about warnings; we only worry about errors.”

This joke is a programming joke. In order to understand it, you have to have a fair amount of knowledge that is specific to programming.

Contrary to popular opinion, when most programmers write code, they write it in a language that the computer can't actually understand. The language that the programmer writes code in is a language that can be compiled (or translated) into commands that the computer understands. The reason for this is that the computer's language is pretty simple, and not very powerful, and most programmers don't want to think about such small details.

The code has to be compiled into computer language, and the code that does that compiling is called a compiler. Compilers take code and translate it into machine language, but if that code has problems with it, then the compiler outputs an error message that tells the human why it cannot be translated into machine language. The programmer has to then fix his code if he wants it to ever get compiled.

If the compiler detects code that can be compiled, but seems likely to cause an error, it will still compile it, but it will also return a warning to the programmer, which tells the programmer that the code is likely going to have bugs.

The joke here, then is that this programmer (and according to him, all programmers as well) do not care about warnings. This is making fun of programmers, and saying that they are not worried about bugs in their code. Sadly enough this is probably true.