Thank you for the update. I hope that you have some leads to go farther with this to help him.
Bessings
Yes my son is verbal. Thank you for the articles they were really helpful. Today was a better day, him not laughing too much at the baby.
Thank you so much for your post. I am gonna look into the websites right now.
Hugs
Athena
My guess is that he is very bothered by her crying and doesn't know how to respond. My daughter shrieks when she hears loud noises that won't stop. I suggest talking to his therapists. They may have some ideas to redirect him.
She has the ability to have like movies running through her mind and has an interesting sense of humor. It rubs off on you after being around her. I say that because her perseveration was insects/bugs and later as she drew them, she would come up with the cutest and funniest drawings. I didn't know this was forming in her at the time when she would respond in unusual ways to things around her and her sister when she was born.
I realized through my experience that on the outside looking in, we are left wondering at the seemingly "odd" behaviors. I think your explaining to your son like you do and conveying that there is a right and wrong way of reacting and that people are bothered by his laughing is one way to deal with it. I did the same with my daughter as we found it annoying at the time to see her grinning and doing mischievous things. She did things like put ice cubes in her baby sister's diaper and toys in her clothes. I had to keep an eye on her. The first time she rubbed her sister's head, she said, "kiwi fruit".
Your son has a new person in his life, your life and your husbands which affects him. He could be reacting this way because of those factors. Letting him know you love him and this new baby girl is important. You have enough love for them both :-) He sees she is important to you all even if he doesn't understand it all, he will be reassured of his place. I am wondering if he laughs at other things?
I am going to include a couple links for you to look at to see if you can explore further if finding something helpful to use.
http://www.sensory-processing-disorder.com/child-who-laughs-at-wrong-times.html
http://www.helium.com/items/1525616-autism-social-skills-facial-expressions-autistic-special-education
I hope you can find something useful.