Is it ensure, insure, or assure?
1. Read The Fucking Source. Variant form of RTFM, used when the problem at hand is not necessarily obvious and not answerable from the manuals - or the manuals are not yet written and maybe never will be. For even trickier situations, see RTFB. Unlike RTFM, the anger inherent in RTFS is not usually directed at the person asking the question, but rather at the people who failed to provide adequate documentation.
2. Read The Fucking Standard; this oath can only be used when the problem area (e.g. a language or operating system interface) has actually been codified in a ratified standards document. The existence of these standards documents (and the technically inappropriate but politically mandated compromises that they inevitably contain, and the impenetrable legalese in which they are invariably written, and the unbelievably tedious bureaucratic process by which they are produced) can be unnerving to hackers, who are used to a certain amount of ambiguity in the specifications of the systems they use. (Hackers feel that such ambiguities are acceptable as long as the Right Thing to do is obvious to any thinking observer; sadly, this casual attitude toward specifications becomes unworkable when a system becomes popular in the Real World.) Since a hacker is likely to feel that a standards document is both unnecessary and technically deficient, the deprecation inherent in this term may be directed as much against the standard as against the person who ought to read it.