grass yass Share definition Flag A term used to describe a person w/ grass on their ass. Supposed to sound somewhat like "gracias." You've been sitting around on the grass for awhile, and when you stand up someone tells you, "You have grass yass!" grass yass by Stephanie :) August 26, 2007 0 0 Get merch Get the grass yass mug. Buy Now — $32.95 See more merch