He begins to speak: "If my mom was a cow and my dad was a bull, I'd be a little calf.

If my mom was a hen and my dad was a chicken, I'd be a little chick. If my mom was

a deer and my dad was a buck, I'd be a little deer. If my mom was a duck and my dad

was a goose, I'd be a little duckling."

After listening to the boy rambling on and on in the same manner for a while, the bus

driver begins to get annoyed.

He turns around and says to the boy: “What if your mom was a drunk and your dad was

a bum?”

In an instant, the boy responds: “I’d be a bus driver.” 
The bus driver probably should have seen it coming!