That's very sad. I really don't know if my teenagers realize how overheated a person or animal gets in a hot car in a very short amount of time. I would be telling them before they drove off with one of my animals, though. We live in Florida, so a great part of the year it's too hot to leave an animal in a car unattended. In fact, my daughter does occasionally take my dog to her apartment, and I have told her not to leave him in the car alone and that it's too hot, but she's no longer a teenager.
We've had several cases of parents forgetting their babies, too, in the last few years around here. And one day care worker leaving a baby buckled in the day care bus....forgot about it.
I never understand it, but my husband says he's so forgetful that he sometimes wonders if he could have ever done something like that when he hears these parents say they forgot the kid was in the car. He never did, though, so I guess he couldn't.
Also, a small kid got in the car playing without the parent's knowledge and couldn't get back out.
On a different note, and not at all tragic, but still forgetful, one of my very good friends had her first child, and the first time they went over to the grandparents to visit, they left at the end of the visit and completely forgot to take the baby. That was the first time they had left the house with the baby. He was asleep in another room, and they left like they always had in the past, just the 2 of them. The grandparents patiently waited for them to remember the child and come back to get him.
On the case of the graduation present, I don't really have an answer. As for me, I usually try not to cause family problems, but I don't know what the right thing to do is.