I don't know if Pesci was the best supporting actor in 1990, but at least he was very very good.
I mean, his role as Tommy DeVito was really just about swearing and kicking, but swearing and kicking is not that easy! if I was there, I would suck in swearing and kicking for sure. What I mean is, you don't need to make an motional role to get an award or something like this.