Some people are so ungrateful

MissJelly
Not sure if this is a CC worthy topic, but not sure where else to put it. 
It really bugs me when people don't even say 'thank you' when you go out of your way for them. One of the things I love most about my boyfriend is his generousity and willingness to take time for everyone. But I do feel he is taken advantage a lot by some of his mates, who are willing to take take take and only reciprocate occasionally. He's not bothered by this as his mates would come running if we asked and he doesn't do things for something in return. The bit that bugs me is their lack of effort sometimes and their lack of thanks. 
Recently we drove another couple and our 2 babies on a 3 hour round trip (we've got a 7 seater car). When we gave them back their babies car seat they complained a piece was missing without checking the seat properly. While still in their driveway my boyfriend pulled apart the car and everything in it for about 20 min while they stayed inside their nice warm house. The. We drive home to check it had t fallen in our drive way. They didn't help and didn't even bother to let us know they found it tucked up in the seat. It really bothered me that my boyfriend went to all that trouble and they were so unhelpful and ungrateful. My boyfriend didn't care. Is this petty?