Smartypants (noun)

1. A person who is overly smart, clever, or arrogant.
2. A person who thinks they are very clever or knows everything.

Origin:

From the phrase "smarty pants".

Examples:

1. He's such a smartypants, always showing off his knowledge.
2. She's always correcting people, what a smartypants.
3. He's always acting like a smartypants and trying to one-up his friends.
4. The smartypants thought he knew everything.
5. She's a smartypants who always had a clever comeback.