Green’s Dictionary of Slang

perfection, excellence, an ideal situation.

1972		B. Rodgers Queens’ Vernacular 198: the tits excellent ‘That tapestry is the tits!’.
1989		H. Rawson Dict. of Invective (1991) 388: Since added to with such common phrases as [...] tough titty, hard luck; and the tits, excellent, the best, great!
1999		K. Sampson Powder 162: You’re in there because they really, really think you’re the tits.
2008		Simon & Pelecanos ‘Late Editions’ Wire ser. 5 ep. 9 [TV script] Herc, you’re the tits. Without your contribution the whole fuckin’ city slips into the Chesapeake Bay.