For one, its a small middle eastern country that, by the look of it from Google earth, is inhabited by white cars only... But no-one cares about that, the term 'Yemen' today is used to describe (usually) a vast amount of epicity in something, whether it be a situation (1) a belonging (2) or somebody's actions (3)
(1) Dude, i heard from Josh that theres gonna be like thirty naked bitches at the pool tonight, they gon break in and have a party, you should come man, it'll be fuckin yemen.
(2) Dude i love your new windows phone, facebook integration, CUSTOMISED COLOURS!? This shit is Yemen!
(3) Ey mang thanks for hookin me in aye, thats some yemeny bro-love there.. Y00 MAI BOI!