Grassy-ass Share definition Flag 'Thank you' in Spanish the way a tourist might say it. Also referring to the behind of someone who sat in a field for too long. Grassy-ass for the crappy Spanish lesson. Don't drag your butt on the ground next time, grassy-ass! Grassy-ass by The Kwoshinator May 12, 2008 0 0 Get merch Get the Grassy-ass mug. Buy Now — $32.95 See more merch