Informal & Casual:
* Bro: (Very common, often used by guys)
* Dude: (Common, can be used by anyone)
* Man: (Common, can be used by anyone)
* Pal: (Slightly more formal than "bro" or "dude")
* Friend: (Simple and direct, often used by women)
* Mate: (More common in British English, but gaining popularity in the US)
* Dawg: (More common among younger people, often used by guys)
* Compadre: (More playful, often used with a sense of camaraderie)
* Homie: (Similar to "compadre," often used by guys)
* Ace: (Informal and affectionate, often used by guys)
More Playful & Affectionate:
* Bestie: (Short for "best friend")
* Chum: (Slightly old-fashioned, but still used)
* Sweetie: (More often used for someone you're romantically interested in)
* Darling: (Similar to "sweetie")
* Love: (Very affectionate, often used by women)
* Sweetheart: (Similar to "love")
* Sugar: (Similar to "sweetie")
Slang specific to certain groups:
* Fam: (Used by some groups to mean "family" or "close friends")
* Squad: (Used to refer to a close group of friends)
The best slang word to use depends on your relationship with the person and the situation.
Remember that slang can be very context-specific, and what is considered "cool" in one group might be considered outdated or offensive in another. It's always best to err on the side of caution and choose words that you're comfortable using.