FF - Too long ago to remember and I only played through it once.

FFII - Hitting myself

FFIV - Dark Elf Cave. Don't get me wrong there's some good story at this point and Toroia's great and all, but there are so many hassles with it. The figuring out what equipment you can and can't have equipped (most is obvious but some isn't). Unequipping and then equipping metal gear ("Metal Gear?" No, not that Metal Gear. Calm doen, Snake). Having to trek to the chocobo forest to get the black chocobo. Then there's the party makeup. Don't like it. 3 fighters (and Cid kind of sucks tbh) and one caster with low MP pulling both white magic and black magic duties. Not fantastic.

FFV - I don't know. The second world? Not a huge fan of this game.

FFVI - Zozo. Towns are for talking not fighting! Also too dark and hard to see routes at time. That or some places in World of Ruin.

FFVII - Somewhere around the Costa Del Sol area tends to get in the Doldrums for me until it picks up again at Cosmo Canyon.

FFVIII - Honestly one of the most consistent games throughout but maybe the desert prison or start of disc 3.

FFIX - Latter part of disc 2, except Black Mage Village being a bright spot and probably most of the middle portion of disc 3.

FFX - Probably around right after fighting Seymour the first time. My memory on the order of this game is a little too off.

FFXII - Starting it. Or maybe right after any of various points in the game where I thought the plot was going to pick up after realizing it just wasn't so... right after Mt. Bur-Omisace, for example, or right after the prison.

FFXIII - Didn't really play enough to have a least favorite part except generally all of it.

FFXV - Didn't really play enough to determine a least favorite part. It was all generally "okay" but not good enough to stick with it to the end.