Grimus Ass Share definition Flag Someone who has an ass like Grimus from McDonalds. I saw this hot chick driving around the parking lot, but when she parked and got out of her car, she had a Grimus Ass!! Grimus Ass by jmb924 October 7, 2011 0 0 Get merch Get the Grimus Ass mug. Buy Now — $32.95 See more merch