Fuck nigga wanna plot, fuck nigga getting killed
That's on my fucking daddy put a nigga in a caddy

from Lil B – Green Card Lyrics on Rap Genius

Meaning

“On my fuckin' daddy” is a variant of “on moms/on mommas,” which adds severity to a statement (the most archaic version would be “I swear on my mother’s name”)
Many Hearses (the cars driven by morticians to transport bodies) are Cadillacs, though not all are.

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