Is it bad if a cat hisses at you when you walk past

Yes it's probably hungry or mistreated

I mean, don't try and pet the cat or anything

No. The cat probably wants you to leave her/him alone. Is the “friend” you’re asking this for, yourself?

Maybe ill or something. I was attacked once by a gf's cat. Siamese cat was hiding behind the door. When I came in she ran up my bare legs to my chest, claws dug in my flesh, her ears were back and she made a guttural sound while looking me in the eyes. Only happened once though

It needs food

from my limited exposure with cats it the kiss of death.......RUN, RUN away very quickly!

Stay away

I like to hiss back at em.

There alwayys really shocked when i speak back in their language lol