Racism isn't funny.
No matter which way you look at it, joking about another pony's race is hurtful and mean; and us ponies definitely aren't about that. It is even hurtful to assume characteristics about a person based off of how they talk or where they're from. The Southern Poverty Law Center is a good resource to look into tracking and confronting hate of all types.
No matter what color your mane is, no matter what part of Equestria you're from and no matter what your neigh sounds like, the herd is a safe place for all bronies.