I started FFXV

[Example]

Great, and should I read the manga too? And get the collectible action figures? Would that help me understand this game I already paid for?

Don't forget the Kenny & Kelly Crow gacha, officially licenced cup noodles and Aranea body pillow, all of which are super important to the plot.

If you watch the Brotherhood episode about him, it explains a little bit of how he can be such a dick to Noctis. However, (1) you shouldn't need a separate anime to explain the motivation of your game's characters and (2) they've been together for several years after that so it was still odd that he went right back to dick mode after Altissia. It's not like Noct sat on the sidelines during Altissia, he was pretty active and suffered a pretty big loss.

One thing that bothered me in the whole game was that if Noctis bumps into him while running around, he gets very snippy with a 'hey watch it!!' which doesn't seem like a good way to talk to one of your best friends.

I especially love how Prompto made such an inappropriate and possibly even offensive joke about Ignis's blindness, yet it was Noctis who told him it wasn't funny while Gladio said nothing. And apparently if you warp strike out of harms way during a fight in that chapter Gladio will chastise you for "abandoning" Ignis, or so I've heard.

Honestly, everything that’s happened in Altissia had been distressing for the whole gang. Gladio has been well established as processing his grief through anger, so it really didn’t seem out of character for him. Did it feel unfair from the player’s or Noctis’ point of view? Sure. But people don’t always behave fairly when in a crisis. I feel it’s less an issue of poor writing and more just genuine character flaws showing through

Yeah but for some reason he really zeroes in on Noctis, like he's always secretly harboured resentment towards him and now finally has an excuse to let it out.