Well in the OG, Barret shouting Shit!! is something that could be better done voiced. It's about the intonation. You could get the point across better in text form by writing Tch or Pff, like he's sneering or putting down something someone says, but saying "Shiit" with the right intonation, it gets the point across. In the game, it just looks like he's going around shouting it randomly in sentences.
Like this. Tifa stops Barret bothering the guy in the train, and he says
チッ!!あんた、ついてるぜ
Shit!! You're lucky.
I think that line would be better with just Tch. Since he's looking down his nose at the guy.