Green’s Dictionary of Slang

tip n.6

[SE tip, the point]

1. the end, the ultimate.

W. Sickert Whirlwind 26 July 67: The raw reader of the rawer art magazines has heard so much about the nobility of the peasant [...] that he has been obliged to conclude that Millet was great because he painted peasants, and that therefore peasants are the tip.

2. (US) the female nipple.

[US] in T.I. Rubin Sweet Daddy 68: Big brown tips [...] nice boobies.

In phrases

on someone’s tip [? the tip of the penis; note on the dick under dick n.1 ]

(US black) of a woman, to be ready for sexual activity, to be (sexually) interested in.

[US]Kid ’N’ Play ‘Last Night’ 🎵 This girl was on my tip.