Su Wong marries Lee Wong.
The next year, the Wongs have a new baby.
The nurse brings them over a lovely, healthy, bouncy, definitely Caucasian white baby boy!
"Congratulations," says the nurse to the new parents.
"What will you name the baby"?
The puzzled father looks at his new baby boy and says, "Well, two Wong's don't make a white, so I think we will name him Sum Ting Wong!