RTFM is an initialism for the direction "Read The Fucking Manual". (sometimes flaming or another metaphor or profanity) This instruction is sometimes given in response to a question when the person being asked believes that the question could be easily answered by reading the relevant user's manual or instructions. In expurgated texts, substitutions such as "read the flaming manual" or "read the friendly manual" are used (or similar variants). Initialisms similar to the one above include GIYF ("Google is your friend") and LMGTFY ("let me google that for you"). These indicate that the item under question can easily be researched on the World Wide Web.
Many alternative expansions for "RTFM" exist (particularly expurgated ones), as do many similarly themed alternative initialisms.
Read more about RTFM: Possible Origins, Context-sensitive Factors in Determining (in)appropriateness, List of Expurgated Expansions