maybe your friend smells
If your cat is hissing at strangers you can't stop your cat from hissing at them. The only thing I can think of that would stop a cat from hissing at someone is letting a cat get to know a person long enough that the cat isn't afraid of the person, and will therefore get along with him/her.
when your cat hiss does it hurt them
Hissing means that the cat is scared and it is trying to defend its self so stay away if a cat starts to hiss and arch his/her back.
Obviously, it didn't agree with your cat!
very carefully
See if the cat has ear mites.
Normally you would hear a hissing sound accompanied by your cat being angry
Maybe he hears a noise or smells something on the other side of the door that he thinks may be a possible threat...
scraching,hissing,meows,purrs,and biting
because they are angry and unhappy and need TLC
Your cat could have a bug or fleas. Make a vet's appointment if this becomes too out of hand. He could be hungry or may see a cat of a different gender and wants to go out to meet them. Good luck!
could be a dominance issue, territory issue or the male is upset for a reason. usually, most animals need a reason to change their behavior. did the sister cat take the brother's toy, favorite sleeping cushion in the window, etc., etc. more info needed. is it at meal time?