It's okay, I like Griffin better though.

What you can do is not tell them your plans for a name, then they can't bother you about it and when the baby gets here then they can't make fun of him for it. That's what my parents did. My grandparents hated my older brother's name, but they got used to it because it fits him so well. This is your baby, not theirs, and if they don't like his name than that sucks for them, doesn't it?
If their opinion matters that much, ask everybody for a list of suggestions and go from there.