Big meanie

My little guy has always been an indoor cat... But he likes to sit at the screen door and see what goes on outside. A couple of weeks after we brought him home, we had a big tom cat coming down to see him through the screen and Dexter would chat away to him. Well he stopped coming but lately we have had this little grey cat, hanging around. We think she is a girl because she is so small, but im also thinking she doesnt eat very well, very skinny...compared to my big boy anyway.
Why is he a big meanie? She had come right up to the door and was watching him quietly as he lazed around (half asleep) i saw her before he did. Anyway when he finally saw her he ran really fast at the door and scared the poo out of her, poor little thing.
Do you think he was being agressive or just eager to get to her? He is quite a social little boy but has more experience with dogs. We are thinking of getting him a playmate in the next couple of months, so I was wondering is this a good sign or not....

Any insight would be great, I am relatively new to cats.

Why don't you adopt the little girl? She sounds like she needs a home. Also, don't be surprised if she shows up with kittens come spring......

As to your kitties aggressive behavior, it may just be playful. You won't know for sure until you introduce. He might be that way anyway with another new cat. It may take a little time for things to go smoothly. But when they do, they sure do enjoy eachothers company.

I'd consider the little girl. I think she needs you......

Was he gowling or vocalizing at all? If it was agressive he probably would have made some evil sounds to go along with the behavior, growling, hissing, etc. I agree with the possibility of adopting the little girl though.

Even if he was being aggressive, he would probably come around after a slow introduction. My mom's one-eyed cat is the only one I've ever known that never learned to accept other cats. My parents adopted some kittens that were under a vacant house and I thought Kitty would love kittens to play with. Only recently, now that Kitty is very old, has she been able to mix with the remaining "kitten".

I don't want to discourage...most of the time, cats adjust to each other after a few weeks. Mine hissed and spit and tried to attack one another at first, but now they are the best of friends. I've mixed many over the years. Kitty just happens to be the meanest cat on the planet earth, so she is an exception to the "one big happy family" rule.

Thanks guys. There were no noises at all, and I have heard him make agressive noises to another cat before. Thats why I think he was just a little over excited.

As to adopting her, it is hard to know whether she belongs to someone else...In australia we have microchips which have the owners details on them, so no collar doesnt neccessarily mean no home. (I dont know if this is the same as other countries) I would hate to start feeding her and start getting attached only to have her owner get angry with me.

She is very skittish, neither me or my partner have got near her. But like I said she was right at the door yesterday and Dexter would have only been about a metre and a half away. She is curious about him, but I dont know if he gave her too much of a fright yesterday for her to come back.