It's a bumper sticker. It says "I Love My Grandcat."
Let's forget, for a moment, all of the sad implications of the message conveyed by the bumper sticker, to say nothing of the fact that someone would actually make such an identity claim by broadcasting it from their vehicle and drive it around town. Let's assume it was a gift from the actual owner of the cat. But, even then, why would ...? Nevermind. Moving on ...
Please try to follow my logic:
"Grandfather" and "grandmother" refer to the parents of my parents.
"Grandson" or "granddaughter" refers to one of my children's children.
"Grandchild" refers to one of my children's children.
"Grandhuman" refers to ... what?
This is my problem with the term "Grandcat". If it had said "I Love My Grandkitten," that would make sense. But "Grandcat" could be the cat of one of my parents, or the cat of one of my children.
So, now this becomes about me. I saw this bumper sticker weeks ago. WEEKS. And it still bothers me. At the very least, couldn't the aforementioned perpetrator of this crime of ambiguity have considered how it would affect people like me? All I'm asking for is a little consideration.