I don't know what it is, but often when I walk around the streets of Sigil or any other city, the locals suddenly turn hostile on me, just like thugs tend to do.
Sometimes they go hostile when I walk past them. Sometimes they attack me when I kill a thug.
Heck, even Reekwind attacked me once.

If I might hazard a guess, are you using spells with an area of effect? If so, it's possible that they are attacking because you were fighting thugs and they got caught in the crossfire. Other than that, I'm at a loss. On a more speculative note, I know other IE games have locals and guards attack you on sight if your reputation goes low, so maybe your alignment is setting it off?

I highly doubt that people get hit by my AoE attacks since I rarely roll a mage character nor do I use such spells.
I also don't think it's because an evil aligment, for my characters tend to be neutral good most of he time.
At least on my latest run, I haven't done anything evil -at least yet- and my aligment appears as neutral good. Yet the locals still attack me.
Lucky for me, it's only a handful of locals that usually attack me and killing them wont mae others hostile (well, not that often, at least.)

Hm... When you say they go hostile, I'm assuming you mean that their aura turns red and they advance on you and start attacking. If all they are doing is going into a tense animation, they tend to do that whenever fights break out or if a hostile gets close.

Yes, their aura goes red and they slowly approach my party and attack me.
I'm aware that they can still go in the ''battle stance'' even if they're not the ones fighting.

Pardon my bad english.

Your english is fine, I'm just baffled by the situation. I got nothing else, sorry.

I suppose I'll just cope with the locals going bonkers.
Thanks for trying to help, thou.

Are you using any unofficial patches or mods?

No, I'm playing the game pure vanilla. No mods, no cheats, no save editors.