Six year old bad behavior

Hi! Looking for some moral support with my newly six year old son’s behavior. For some background he’s excelling in kindergarten and doesn’t have any issues in the school setting. His teacher tells me he’s a great listener and helper 😂.

Where we are struggling is in social settings, he has a holiday birthday and gets almost feral and crazy around gifts. It was an embarrassing Christmas at a family members house when he threw fits until he could open all his birthday and Christmas gifts and then continued to to whine. And most recently we went to visit my elderly grandmother in her nursing home who was looking really looking forward to seeing him. He proceeded to act out the entire time and barely acknowledged her. It was incredibly painful as I know he's a good kid and can't wrap my head around this behavior. We correct him in the moment when he acts out and also discuss our expectations before going to outings. We’ve also taken away privileges (treats ect) when he comes home after these incidents.

Lastly, I think he is a deeply feeling kid as Doctor Becky would say and always has been but this behavior is appalling and I'm starting to think I can't bring him anywhere.