Green’s Dictionary of Slang

tuna n.

1. (US) one who believes themselves to be far more sophisticated than is the reality.

[US]Current Sl. VI.

2. (US gay) a homosexual sailor who only takes the passive role in fellatio.

[US]B. Rodgers Queens’ Vernacular 23: If he sells only his penis, he is a salt-seller, shore dinner or tuna (a delicious sea product).

3. (US campus/gay) an attractive man; thus hot tuna! an excl. said on seeing a sexy man.

[US]B. Rodgers Queens’ Vernacular 110: hot tuna (exclam, kwn NYC, ’71) superlative reserved for sexy men.
[US]Eble Campus Sl. Apr. 4: tuna – good-looking male.

In compounds

tuna (fish) (n.)

1. (US campus/black) a girlfriend, a woman.

[US]Current Sl. I:3 8/1: Tuna, n. A fat girl.
[US]Eble Campus Sl. Mar. 4: tuna – girl.
[US]E. Folb Runnin’ Down Some Lines 151: Women are not only characterized as land animals but as fish – trout, fish, tuna fish.
[UK](ref. to 1991) Morgan & Neil Teaching modern Foreign Langs 285: Fall 1991 A total of 79 terms about women [...] This reflects the importance of women's looks over almost everything else about them, except sexual activity: butch, GG (gangster girl), heifer, hellpig, hiddie, hobag, scud, tuna.

2. (orig. US black) the vagina, both positive and negative.

[US]E. Folb Runnin’ Down Some Lines 151: Sweet tuna! I’m Charlie Tuna, I’ma gonna git me a piece that nice meat! I don’ care! Dark meat, light meat, am’ no difference to me. Pussy’s pussy! [...] Tuna, that be some stanky pussy. She on d’ rag!
[US]Eble Campus Sl. Fall 2: fishy/tuna fish – women’s smell.

SE in slang uses

In compounds

tuna taco (n.) [taco, a Mexican cornmeal pancake]

a woman’s genitals; esp. in the context of cunnilingus.

Stan B. on Urban Dict. [Internet] tuna taco Another name for the female genitalia. I think I’ll go get me some tuna taco tonight.
[US] ‘The Cooter Monologues’ at www.pinkhairedgirl.com 20 Jan. [Internet] Tuna Taco, Roast Beef Curtains. Both of those terms gross me the fuck out. Because they’re nasty and disgusting!
tuna wagon (n.) [its only use would be to convey fish]

(US) an old, decrepit car.

J.P. Kelly ‘Monsters’ in Isaac Asimov’s Science Fiction mag., June [Internet] Riding a tuna wagon down the mean streets was bad enough, but what really spooked him was Celeste’s driving.