J cough?

Jack off, I'm afraid.

Interesting, I wonder which type of English speakers would see that as their initial hunch for pronunciation.

While Oscar Wilde would undoubtedly have something witty to say about that, I guess it's a matter of stress: if you read it as a word and assume stress on the (invisible) first vowel, it's almost inevitable: juh-cof.

But we dont say juh sahn for JSON? Hence why Jcough seemed intuitive.

Language is not very deterministic. An unknown word can remind you of more than one other word, which can influence the way you pronounce it, certainly in English where pronunciation is so irregular. That’s not a fact of course, just a possible factor.

Guess you could say if its a 'jack off' here, its 'jiss on' there.

There is a very, very small difference between placing a slight break in the middle of the acronym as J-COF or as JC-OF, because there's a major unwritten vowel sound after J in any case.