The growth of fuzz, hair, or fur on the lower back entering to the domain of one's buttocks; usually pertaining to the male race, but also including rather masculine females
American Man: Why, what is that lawn of hair on your lower back that?
European Woman: I think they're calling it assgrass.
Much like an assumption but instead of making an ass out of you and me, the person simply makes an ass out of themselves.
Guy1: Do you like fishdicks in your mouth?
Guy2: Nah fishsticks are gross Guy1: AHAHAHA what are you a gay fish?
Guy2: What are you talking about
Guy1: Wait did you say no? ....shit
Guy3: dude way to assurself