Playful:
* Brain: "That kid's a real brain!"
* Smarty pants: Often used ironically, "You think you're so smart, smarty pants?"
* Whiz kid: Usually refers to someone young and talented.
* Guru: A master in a particular field.
* Rocket scientist: Implies someone is extremely intelligent, often used humorously.
* Brainiac: Often used in a positive way, but can sometimes be seen as condescending.
More Serious:
* Mind-blower: A person who is very insightful or has groundbreaking ideas.
* Visionary: Someone who has the ability to see the future or has innovative ideas.
* Polymath: A person with expertise in many different fields.
* Prodigy: Someone with exceptional talent at a young age.
* Gifted: Possessing exceptional natural abilities.
Slang specific to a particular field:
* Hacker: In the tech world, someone who is very skilled at programming and problem-solving.
* Guru: Can be used in many fields, but specifically refers to a master in a particular area.
It's important to remember that slang can be subjective and the meaning can vary depending on context and region.