Why is everyone so aggressive?

Maybe just me but today I saw someone who looked tired and I said in worried tone. You look tired to start some conversation and thought maybe the other girl working the cash register and who did have bags under her eyes would be like yeah they're overworking me to death here or something like that a dark joke. Some older lady came behind my back and said excuse me! She looks fine to me and then got all aggressive and in my face and wouldn't let me speak and I said I didn't mean it in a rude way and quickly left.

This has happened so many times to me but I never understand why and I just try to act normal in them. I asked another older lady at my work as to how the office usually runs with seating arrangements here because I was very new to the office and she started saying why should I know and she said it in a mad manner as if I ruined her day. She had her arms crossed and looked at me pissed.

I said I was just asking because I was new and she said yeah like I told you before how would I know? Like why are you even asking me and she just started laughing and I just quickly just said I'm sorry and left. Like you could have just walked away and said no and you didn't have to make it like that.

Maybe I'm just overreacting, can someone tell me.