The joke depends on a real quirk of language, since inflammable and flammable both describe something that can catch fire, even though the prefix looks like a negative. That oddity has been used for decades in comedy and everyday complaints about confusing words, and the Spanish phrasing inflamable significa flamable turns it into a compact shareable clip. Online, the line circulates in the shorter misspelled form inflamable flamable, which helps explain its search popularity, and it survives because the same confusion still catches new listeners out.