We caught up with Cube at LAX, and he couldn't be more UNimpressed with his placement at #18 on the list ... dismissing Billboard's hip hop authority as a staff, chart and magazine!!!

Billboard released the final rollout of its list on Thursday, ranking Jay-Z at #1 and featuring Eminem, Drake and Nicki Minaj amongst the top 10 ... but Cube still didn't care.

Cube dismissed the BB editors even further for snubbing his Mount Westmore bandmate Too $hort altogether -- while the rest of the group, Snoop Dogg and E-40, did make the rankings.

The N.W.A pioneer has never been one to bite his tongue when it comes to critics, and he told us all these silly lists "are like a**holes: they all got one and they all stink."

Cube says he'll stick to his own list. Check out the vid to see where he ranks himself!