“You are worthless!”
This is possibly the worst thing you can say to a child. Especially when you are the person and the mental figure they expect most of to be given approval of. By saying this, you are putting your child on a never ending journey to seek approval from the outside world. Instead of helping them find their own worth inside, you are letting them believe they have nothing inside to find.

There are so many things you can say instead of this, like: “You can do better!”, “Nobody is perfect.”, “It’s not your day, you’ll do better next time.”

“Big boys/girls don’t get scared!”
First of all, why are you lying to your kid. You are probably more frightened than they are throughout your day. Second, you are forcing them to reject what they are honestly feeling. Fear is not a bad thing, it reminds us when to be careful. You should not run away from it but face it, be aware, learn from it. And real courage is not being fearless, but facing your fear even if you are terrified.

Instead of this, tell your kid: “It’s ok to be scared buddy. All of us are scared sometimes. But I know there is courage inside you that will help you do the right thing even if you are scared. You are my little hero!”

“I am disappointed in you!”
Parents usually tell this to their children when they already feel bad. Trying to make them responsible for your disappointment is pretty selfish. You can be disappointed in a friend, you can be disappointed in a movie, or even your country’s politics, but you can’t be disappointed in your child.
You are there to let them on a right path. So when they do something wrong, guide them back. Your disappointment is in your guidance, not your child. Teach your child what that they did is wrong and why.

Instead of this, tell your kid: “What you did is wrong, in my opinion. And I believe you made an honest mistake. Even if you chose to do what you did, I can assure you’ll realize it’s wrong after I explain. I know you can do better!”