Slang for "for sure". Though most people attribute it to Snoop Dogg, fo shizzle can be traced back originally to E-40 from Vallejo, California. Bay Area like what.
While originating out of hip-hop culture, this phrase has been overused to the point of triteness. Its most famous usage is
A bastardized term that is by most of the population thought to mean "for sure" or any number of agreements. The true meaning, however, is "I concur with you whole heartedly my fellow African brother."
Ghetto black man: "Fo shizzle my nizzle!"
Rich black man in response: "I concur with you whole heartedly my fellow African brother."
Ghetto black man: "..."