Green’s Dictionary of Slang

1. (US) a pimp [negative stereotyping of the proper name which is Fr., like alphonse n.² ].

1935		A.J. Pollock Und. Speaks.
1939		D. Maurer ‘Prostitutes and Criminal Argots’ in Lang. Und. (1981) 117/1: box-coat. A pimp. Also [...] Louis.

2. (UK drugs) one sixteenth of an ounce of cannabis [play on French King Louis XVI].

2001

OnLine Dict. of Playground Sl. 🌐 louis n. Want to buy a louis?, Refers to a sixteenth of an ounce of hashish, which has always been a popular drug in playgrounds.

3. (US campus, also lou) an unattractive man.

1989

P. Munro Sl. U. 124: lou/louis ugly guy.

4. (US black) any luxury item produced by the firm of Louis Vuitton.

2017		Young M.A. ‘Walk’ 🎵 Louis pack got me buggin' out / Louis scarf, gotta thug it out.
2020		G. Krauze What They Was 45: They only rate ballers [...] man who are trapping and making p’s and rocking Gucci and Louis and Balmain.