"Be Careful What You Teach Your Children" joke

There once was a boy, whose parents was a cursed a lot.
One time, while he was on a drive with his dad, a policeman pulled him over and gave him a ticket. "Bastard!" the father muttered afterwards.
The boy asked, "What does 'bastard' mean?"
The dad told him nervously, "It's a slang word for 'police officer'."
Another time, the dad was walking out of the house. On his way out, he tripped over the doormat and yelled, "Shit!"
The boy heard and asked, "Dad, what does 'shit' mean?"
The dad said to him, "It means 'doormat'."
Later, the boy went into the kitchen and his mum was cooking eggs. She dropped one and yelled angrily, "Tit!"
The boy asked her, "What does 'tit' mean?"
The mum told him, "It's another word for 'eggs'".
The dad came back home later and went upstairs. The boy followed him up. The dad went into the bathroom, closing the door behind him. Seconds later he cut himself shaving and shouted, "Fuck!"
The boy asked him when he came out, "What does 'fuck' mean?" The dad told him, "It's another word for 'shaving'."
A few days later, the doorbell rang and the boy answered the door. A police officer was standing on the porch. The boy, smiling said, "Hi bastard, come in! Wipe your feet on the shit. My mum is in the kitchen frying her tits and my dad is upstairs fucking himself."