Apparently my family is racist...

Apparently my family is racist. I had them meet my new black girlfriend and they all got mad and started screaming at us...

Especially my wife.

The humor in this statement is that the jokester misunderstood why his family was getting mad at him. The real reason why they were getting mad was that the jokester was married, and shouldn't have had a girlfriend - not because his girlfriend was black.

I found this joke moderately funny.