(Originally on comp.lang.perl.misc, but may have spread):
A question which answers itself. A sure sign that the questioner is too lazy to think or open the manual or a book. Also common on perlmonks, the archetypical self-answering question is "How do I find the length of a string?".

Non-Perlers might not be aware that length STRING returns the length of a string. The question manages to contain its own answer; it is impossible to manage not to find it!