What You Think You're Saying: "Life is too short short to waste your time worrying about the little stuff. Let it go and you'll feel a lot better!"
Why It's Actually Pretty Annoying: If you need to tell someone to not let something get to them, it means that it's already gotten to them. They're not looking for advice on how to feel. They're looking to vent about how the feel already! Telling people what they should do when all they want is someone to listen to them might seem helpful, but it's actually just a little obnoxious.
What You Should Say Instead: "That really sucks. I'm sorry!"
What You Think You're Saying: "Be happy and you'll feel better!"
Why It's Actually Pretty Annoying: Trying to force happiness is the most useless waste of breath imaginable. Saying "Smile" or "feel better" is along the same lines as a someone coming out and saying "I've figured out how to fix world hunger: We should give the hungry people food!" Just because the solution is obvious to something, doesn't make it easy. If someone isn't smiling, it's not because they didn't realize they would feel better if they were happy. It's because they, like all people, have feelings that they have to work through sometimes and nobody can force their emotions."
What You Should Say Instead: "Let it all out!"
What You Think You're Saying: "I love you so much that your pain is my pain!"
Why It's Actually Pretty Annoying: The phrase, though well meaning, is a weirdly blamey thing to say to someone you're trying to console. It's like saying "On top of what you're already upset about, I'm gonna make you feel bad about how it's personally affecting me!" If you're ever in a place where you need to say it, that means it's probably not a situation that you should be injecting yourself into in any way.
What You Should Say Instead: "I'm here for you if you need me!"
What You Think You're Saying: "I have a funny little thing to tell you!"
Why It's Actually Pretty Annoying: Telling a person that you remind them of someone or something is a good way to instantly make that person more self conscious than they've ever been. No matter how flattering the comparison may seem, they will instantly find a way to take it as an insult. You could a person "Hey I saw Brad Pitt riding on the back of a golden lion and thought of you!" and they will find a way to take it like a personal insult.
What You Should Say Instead: Nothing. Literally nothing you can say in this situation will end well.
What You Think You're Saying: "I'm empathetic."
Why It's Actually Pretty Annoying: BECAUSE YOU DON'T KNOW HOW THEY FEEL, DUDE! You might have an idea about how they feel, but unless you can literally enter their mind, you can't say for sure you know how they feel. No person on earth has ever been consoled by the knowledge that they aren't special. Just let people have their moment before reminding people that you too have had problems before.
What You Should Say Instead: "Tell me how you feel."