An acronym standing for "Fuck Your Honda, Nigga!"
A pejorative used against Honda Civic owners. The term became popular during Forum Wars TV show, Season 2 (2011), when a Mazdaspeed 3 with 260 HP from mazdaspeedforums.org was pitted against a Honda Civic Mugen with 360 HP from 8thcivic.com. The Mazda was victorious in ALL events. The driver of the Mazda, with a wink, told the TV show producers the acronym meant "Fix Your Honda, Noob." The producers still included the FYHN acronym in the TV show whenever they showed the Mazdaspeedforums.com logo. It's believed they did know what the true meaning of "FYHN" was.
FYHN, you just got schooled by an old guy driving a wagon