A fixed amount of entertainment or amusement that must be met by a single individual. It usually involves drinking copious amounts of alcohol until one nears blacking out. Easiest way to reach your fun quota is simple: just have fun and don't be a pussy.
Kirk: I'm almost at my fun quota. I just need a few more shots.
It's a reference to a song "Fastlane Youngstas" by Los Angeles rapper, Nipsey Hussle. It's on the album Bullets Ain't Got No Names Vol. III. The term describes a person who's been through the struggle and whose primary concern is living a gangsta life and making it on top.
Fastlane Youngstas, We Fly or We Die.
Larry: Tron's a fastlane youngsta. I love that man.