Sometimes users ask to be blocked. Wikipedia's blocking policy says that "typically, such requests are refused." Typically they are, but not invariably. Some administrators, including myself, are willing to consider placing self-requested blocks.
Don't request a block if you're not sure you'll feel the same about it down the line. Perhaps a wikibreak using the wikibreak enforcer will serve your purpose.
The requirements listed below are my personal standards for placing a self-requested block. Requests meeting these terms may still be declined at my discretion. Requests may be made by e-mail or on my talk page. E-mail requests will be taken in confidence, up to the point where I actually place a block. The block log will of course give user request as the block reason.