I don't mind people boasting about their grandchildren, but I really don't like it when people try to trump others. This happens in one group I belong to. Someone says that their grandson has got his first car, which is a second hand Corsa, and someone else has to point out that her grandson has a Porsche. Or one person is delighted that her grandchild has just got a degree and another 'casually' mentions that hers got a First from a 'top Oxbridge College'. It's one thing to be proud of your grandchildren, but putting others' loved ones down to do it is mean-spirited, I think.
There is a subset of people in what is otherwise a lovely group whose grandchildren (like their children, their husbands and their pets
) all got 'brilliant' exam results from 'highly selective' schools, and are doing 'exceptionally well' in their 'top' jobs with 'excellent' prospects. That sort of boasting is tedious, but a general sharing of grandchildren's lives is lovely, if it doesn't go on too long.