Katie,
I agree with so many of the other moms, and Sherry has a good point, he needs to be polite. We are free to not like certain things in our lives, but they are what they are and it doesn't give us the right to be rude about them. Yes, there's lots going on around him so maybe his summer isn't going like he'd like it to, but he has a home to live in, food to be eaten, gets to go to a pool...lots more than many children his age have.
Thankfulness is something we should be practicing 365 days a year, not just during Thanksgiving week, but many children don't see that. I don't know that you would be open to something like this, but my nephew was getting the same way a little before he turned 9, so dad started taking him with him to feed the homeless at a motel. There's many children living there, so he sees them eating what they're served without complaining, and going through bags and boxes of used (but clean and usable) clothing, shoes and toys. They'll be doing a giveaway next month, the children will each receive a new backpack filled with necessities for going to school ~ paper, pencils, pens, crayons, etc., toothpaste and toothbrush, a hairbrush, a new outfit and a pair of shoes. When my nephew saw this last year he was truly humbled, they received just a fraction of what he takes for granted and were happy, he said they acted like it was Christmas. Many organizations take donations of supplies for projects like this, perhaps you could locate one near you and the two of you could go shopping for the things you'll be donating. This would give you a platform to point some things out to him.
He may not be throwing a full-fledged tantrum, but making the disrespectful noise, throwing his arms up and crying for a better life sure are the beginnings of one. I'd have replied I didn't appreciate being spoken to that way, and that the next time (and subsequent times) he did he would be going to sit in his room, not allowed to play, and would come out when he was ready to apologize for his rudeness. Another option would be to lose a privilege he'd been looking forward to, like an outing or new toy.
I would also make sure that everyone practices being polite and considerate of others in the family, using "please" and "thank you" when asking or receiving anything. He's old enough to get his own snacks, just make sure they're within his reach, and he's not too young for you to ask him to get you one. Maybe some responsibility will help him see what you're trying to convey to him.
Check out your local library for books on manners, responsibility, and thankfulness, the children's librarian can point them out. Summer is a great time to read and learn in a relaxed way, you can talk about the books and use them to illustrate points you're trying to get across to him.
And just remember, your guidance and pointing things out to him will turn him into the considerate, thankful, respectful, helpful young man you want him to be❤