fr fr no cap

The phrase "fr fr no cap" is a shortened way of saying "For real, for real, no cap". "No cap" is a slang term, meaning "No bullshit", "No shit" etc. and it is commonly used to signal the fact that some kind of information is not false. Therefore, "fr fr no cap" is a phrased commonly used by Gen Z's to signal the same thing: the fact that some kind of information is not false.

"Bro's actually braindead fr fr no cap!"