Autistic people are known for being blunt (meaning honest, but sometimes telling people things they don't want to hear), having trouble figuring out how other people are feeling (not realizing someone is upset), and having trouble reading social rules. This combination can accidentally make things that kids on the autism spectrum say sound "mean," even if they didn't mean to be.
For example, somebody autistic might see two friends joking around with each other and calling each other 'bad' names for fun. Kind of like Jimmy and Cindy do on Jimmy Neutron - they say bad things, but they actually like each other. Then the autistic kid might think it's okay to call people bad names, and maybe call someone a 'bad' name without the signals of body language/tone to suggest they're joking.
Here's an example I took from Jimmy Neutron:
Cindy: Ha! Neutron probably thought the low gravity would throw off my backswing. Wrong! As usual.
Jimmy: Hey! How about instead of bragging, you thank me for inviting you along at all?
Cindy: You're right, Jimmy. Thank you...For letting me kick your butt on the back nine!
Jimmy: What is your problem, Vortex?
Cindy: I don't have a problem! What's your problem?
Jimmy: Oh, I think you do have a problem!
They aren't actually made at each other - Jimmy and Cindy just like arguing for fun. And it's okay because everyone knows they're doing it for fun, and Jimmy and Cindy are best friends. Now imagine if an autistic kid said some of those things to someone in a different situation - maybe to a kid in their class that they weren't friends with. All of a sudden, those same things aren't okay to say anymore and they could get the autistic kid in big trouble! And other kids might start thinking the autistic kid is mean, when it was actually just an accident.
If an autistic person makes too many mistakes like this, they may end up being labeled a "bully." In our schools, we don't like kids who bully other kids. What we do like is kids who fight back against bullies. So what happens is a kid who wasn't actually trying to be mean or a bully ends up getting seen as a bully...and then the autistic kid ends up being bullied.
Ignoring them. Gossip. The silent treatment. Talking about the autistic kid like they're not there. Telling people they shouldn't be friends with the autistic kid. Each of these I have witnessed happen to a "bully" on the autism spectrum. When I first saw this, I was watching a move about real life where an autistic girl was accused of bullying. She was summarily kicked out of her summer camp and ostracized - but when asked if she was bullying she didn't know what the person was talking about.
When I came to college, I had a friend something similar happened to. She made some comments, which accidentally sounded mean, but really were just her trying to make jokes. After that she was gossiped about, isolated, given the silent treatment, and people were told not to be friends with her. Later, I saw the roots of something similar happen with another one of my friends, this time a guy. He asked a question and, thanks to his not having read the situation right, put another person on the spot, which made them angry. That's a situation which would have been prone to retaliation and bullying if we weren't all already good friends.
After having seen all this, you'd better believe that I tried everything I could to make sure it didn't happen to my sister Caley, who's also autistic. I thought she was safe. And, yet, in her case kids also thought that her social mistakes which made her accidentally sound mean at times, were bullying and then the "bullied" kids talked about her behind her back and ignored her. Are you seeing a pattern here? Me, too, and it's one I'm determined to put a halt to.
'That was so obviously mean, how could (s)he not get it?' you might ask me. Autistic people won't just "get" something because it's obvious to neurotypical (non-autistic) people. Autism is not something that just goes away. That said, autistic people are no more or less likely to be a bully than you or I are. Actually, the number of autistic people who are bullies is about the same as it is in the general population - that is to say, quite low - and some say it's even lower than that.
While the number of bullies may be similar to the general population, the number of kids who have been bullied is not. Almost 50% of autistic kids in middle and high schools, which is WAY more than other kids.
Even though society encourages us to fight back against perceived bullies, it strongly discourages us from bullying those who are disabled. So why, then, are people on the autism spectrum so often bullied? A study found that people with 'high-functioning' autism are bullied at a higher rate than those who are 'low-functioning'. That's because a lot of times people don't realize people with 'high functioning' autism have a disability...which means kids just think they're 'weird' and that it's okay to bully them. (It's never okay to bully anyone.)
So what can you do to help? If you see bullying, speak up and tell an adult. Easier said than done, I know, but you don't have to fight it alone. In schools, teachers, guidance counselors, and administrators are all great resources. Simply report the bullying to any them, and they can handle the situation from there.
What I've done in the past was actually talking to the bullies themselves (not when I was being bullied, when I saw someone bullying someone else). Yes, they're doing a bad thing, but odds are they're not bad people - some people don't see what they're doing as bullying, just as 'fighting fire with fire'. If you tell them what you're worried about, they may realize they should stop acting the way they are.