"AF", a rather solid candidate for its origin might be from WWII, as per dialogue hereby portrayed in the TeleVision-series: "World War II in HD Colour" by ๐ฅ๐๐๐ถ๐๐ฝ๐ถ๐ ๐๐ถ๐๐๐พ๐, S1:E5: "Red Sun Rampant "at time stamp: 31:26 - 32:14; "Target AF"... rather the mysteriously unknown meaning of "AF". It took the US approximately north of 48 seconds to figure out such meaning: 32:14: "Admiral Chester Nimitz now knew exactly..."
Nauticans: "they had no ID where Target AF was"
Pronounced as 'aff'. The abbreviation for 'As F*ck' but used in conversational sentences as a single word.
It's used to empower the effect of sum shit, whatever it is
-I'm tired af
-Eurovision this year wuz lit af
-u boi sweet af