Boy only listens when it benefits him

So we stop to get Ice Cream at about 6 o'clock at night. Yes, this will spoil everyone's dinner, but we're on vacation and it's a beautiful night. We walked about 2 miles on a jetty cutting right through the ocean, me with girl strapped to my back in one of those little kid backpack things. They're awesome, by the way, I highly recommend. Anyway, we're all pretty tired, Girl is sound asleep in the back of the car. We get our ice cream in shifts. I take boy first. He gets a cup of moose tracks. I get a blueberry cone. Yes, I'm lame, I don't get the flashy flavors. We go back to the car and Mommy goes to get her ice cream. A group of about 10 people had formed behind Boy and myself, so I figured Mommy had a wait. The girl at the counter had efficiency issues. Boy pounds his cup of Moose Tracks. We like to share, so that means he also eats a bunch of mine. We're both finished by the time Mommy comes back. She eats most of her cone and we get in the car. A few minutes later, Boy decides it's time for Mommy to share. "Just a little taste," he says. "I won't even eat any of the cone. You're not sharing. You need to share." Throwing it right back in our faces, he is. This goes on for a good 5 or 10 minutes. Mommy has a limit. She hands him the cone. Within about 10 seconds I hear a crunch. That little liar. He goes to town on the thing, claiming he's entitled. I manage to snatch the last little bit of cone with the liquid chocolate ice cream soup in the bottom from his grubby little hands for Mommy. The chivalrous gentleman I am. Mommy's pretty disgusted at this point. She eats it. He cries for 10 minutes. As if I did something wrong. "Daddy hurt my feelings. Daddy grabbed. You shouldn't grab." I'm not sure if I'm sorry I grabbed or if I'm sorry we didn't stop at a second ice cream stand and eat an entire ice cream cone in front of him and not offer him any of it while I commented how the ice cream was better than the ice cream at the first ice cream stand.