Your kid is entitled (and by your kid, I mean my kids). He's so entitled. You give him a toy plane (oh, I don't know, for example) and instead of saying thank you and playing with the plane, he finds some way to make an issue out of it so he can tantrum. Perhaps his sister's plane has more green on it (you know, for instance), or he can't fly it perfectly the first time he tries (like I said, just throwing things out there. Sigh.)
Or, hey, you bring your kid shoe shopping. You get her the ridiculous Princess Sophia sneakers she wants that light up a million different ways. You also pick out a pair of dress shoes, some purple low boots, and some cute knee-length boots. But the knee-lengthers weren't on sale like you thought, and you have enough shoes without them. Instead of recognizing that she now has three new pairs of shoes, and she should be over the moon about her new fashionable self, she's super upset about the one pair she couldn't get.
Never ever buy them anything again or do anything nice for them because seriously what the hell.
Okay, just kidding.
Look, they're just exhibiting patent human nature. We always want more than we have, and when we're rewarded for things, or get treats, we assume we deserve all of it and more.
As parents, we have to teach our little jerks, I mean kids, how to show gratitude.
I'm making it really simple for mine. Every time they pull this entitled crap with me now, I remind them gently what to do instead.
"Mommy just ________ for you. What is the correct response?"
Nowadays they know the answer, but I had to train them to get there. Then (hopefully) they remember themselves, say thank you and we move on.
If they don't, well, I take the toy and the shoes and whatever else they're being miserable about away. Because honestly, people. The correct response is thank you.