Similar to the rule of thumb. The rule of thumb was that it was legal for men to beat their wives as long as they used a stick no wider than their thumb. Some women take offense to the use of this phrase. Rule of wrist is much more appropriate for these nit-picking femanazis.
The rule of wrist here is to measure out an arms length.
by Dave November 17, 2003
Popularized by the film "The Boondock Saints", The Rule of Wrist is a fitting male translation of the original rule, "Rule of Thumb", which is; a man can beat his wife as long as the stick was no wider than your thumb, after drunken review, it was decided that a stick as wide as your thumb cant lay out proper punishment and the width of your wrist should be used instead. upon mentioning this to a female in a serious tone of voice, expect to be kicked in the testicles.
"Cant do much damage with that now can we? Prehaps it should have been Rule of Wrist?"
by KaiTenSatsuma [KTS] April 07, 2007