Being sure of yourself is a good thing, until it isn't. English has different words for each side of that line, and mixing them up can insult someone.
Way 1 · best compliment
Believes in their own ability. Always a compliment.
Examples
She's a really confident speaker.
You looked so confident up there!
In a conversation
A: I was so nervous up there.
B: Really? You looked so confident!
Common mistake
Not: You are so confidence.
Say: You're so confident.
"Confidence" is the noun. To describe a person, use the adjective "confident".
Way 2 · calm and steady
Quietly sure of themselves, never showy. Common in references and reviews.
Examples
He's calm and self-assured with clients.
For someone so young, she's remarkably self-assured.
Way 3 · could go either way
Depends on the tone. Said with a smile it's praise; with raised eyebrows, a warning.
Examples
He's very sure of himself for a first-year student.
You're very sure of yourself, aren't you?
Way 4 · showing off
Too confident and loves to show it. Often about young people or sports stars.
Examples
He scored once and got really cocky.
Don't get cocky. The second half is still to play.
In a conversation
A: I'll beat you easily. I haven't lost all year.
B: Don't get cocky. You haven't played me yet.
Way 5 · self-important
Thinks they're very important and talks about themselves a lot.
Examples
He's nice, but a bit full of himself.
She talked about her own success all night. So full of herself.
Way 6 · looks down on others
Thinks they're better than other people and treats them that way. A strong criticism.
Examples
Our new manager is so arrogant. He never listens to anyone.
I don't want to sound arrogant, but I knew I'd get the job.
In a conversation
A: How's the new boss?
B: Honestly? Arrogant. He never listens to anyone.
Common mistake
Not: She's very proud. She thinks she's better than everyone.
Say: She's quite arrogant. She thinks she's better than everyone.
"Proud" is often positive in English ("proud of my son"). For looking down on people, say "arrogant".
Read the moment, then choose the way that fits it best.
Pick one and practise it in a real conversation. Save the ones you want to remember.
