Green’s Dictionary of Slang

1. muscular, well-developed.

1996		Eble Campus Sl. Sept. 4: jacked – in good physical condition, toned: ‘After working out at the gym for six months, Nicole was jacked’.
2003		Eble Campus Sl. Nov.
2005		Mad mag. July 14: He’s also super-rich and his body’s jacked.
2011		C. Faust Choke Hold [ebook] Her body was flawless, jacked and shredded.

2. of coffee, caffeinated.

1996

Eble Campus Sl. Sept. 4: leaded – caffeinated [...] Also high octane, juiced, jacked.