Okay mommas I need help.. my son is 4 and just started the “it’s mine” phase. I don’t know how to…

Okay mommas I need help.. my son is 4 and just started the “it’s mine” phase. I don’t know how to handle it. We went on vacation this last weekend and he was a horribly behaved child and I was so embarrassed because we went with my dad and he was so stressed out by my son. He didn’t listen at all (and I mean AT ALL) and then when we went to eat the waitress gave him and my 10 year old sisters (twins) crayons to share and my son screamed saying the crayons were his and my sisters felt bad so they just gave them to him and no matter what I said to him he wouldn’t stop screaming about the damn crayons!! He has never had a problem sharing anything until now.. pleaseee all advice is welcome!! I’m desperate here!!!