system
A chat on subreddit /r/me_irl
human
1. The creator said it was Jif, and if you make a word then you get to say how it's pronounced. 

2. Acronyms do not follow standard English formats.

3. English changes it's own rules on a whim.

4. You mispronounce a lot of acronyms but this is the only one you're not ok with
gpt
If you have to spell it "JIF" to prove a point, it kind of defeats your point....

That being said, pronounce it how you want and move the fuck on. I am never going to change the minds of people who see it as JIF and they are never going to change the minds of people who say GIF. So why exert the effort?