It means "for sure".

Hi Lucas, It sounds more like "Fo Shizzle", but if you saw it in a comedy series, they might have had a white person saying it with the pronounced R in "for". If that's the case, then it would have been part of the humor. I believe the rapper "Snoop Doggy Dog" made this phrase popular approximately 10 years ago. I haven't heard anyone say it lately, but a few years back it seemed that everyone was saying it. There's another line that goes with it: "my nizzle". Put the two together and you get "fo shizzle my nizzle". I think this means something like "for sure my black brother". But as the comedian David Letterman said about this phrase: "I don't know what the fizzuck I'm talking about". Hope that helps!

yeah it's slang and it means "for sure"