Green’s Dictionary of Slang

1. (US black) a black person or a Puerto Rican.

2000		P. Beatty Tuff 74: You call a moreno you don’t know Papi, B, or G, but Puerto Ricans is strictly B, whether you know them or not. A Puerto Rican rarely calls another Papi in public, but a non-Rican trying to be down can call another Rican papi and maybe get away with it.
2000		Blackboiz for Other Boiz 🌐 24 Mar. I like hard up thuggish masculine papi’s with great tight or muscle bodys, must be str8 acting.
2015		J. Spades ‘Anytime I Want’ 🎵 Feeling like it's '09 again / Telling papi I need consign again.

2. used as a term of address (race-irrespective).

1996		L.A. Times 19 Sept. E1/3: As a term of endearment ‘papi’ means many things to many people. For intance a mother may tenderly call her child papi (my son); a daughter might proudly say her father is her papi (my father); a wife can label her husband her papi (my old man) or a friend can shout ‘Hey, papi!’ (Hey, dude).
2010		Codella and Bennett Alphaville (2011) 13: [to an Italian] Hey papi [...] Can I get another glass of water.
2012		J. Díaz This Is How You Lose Her 21: Asking her, Where are the stars? And she said, They’re a little lower, papi.
2017		D. Winslow The Force [ebook] ‘Are you filled with remorse now, papi? Irish Catholic guilt?’.
2021		S.A. Crosby Razorblade Tears 183: ‘Who I am doesn’t matter, papi’.