My (23F) FIL (70M?) spanked me, and my husband (30M) thinks it's not a big deal and thinks it's "kind of funny". And, I'm freaked out and rethinking our relationship. What do I do?

Lol she can't drive so there's no way she's leaving her husband or calling the police on his family. Grandpa put her in her place and that's it period. She'll not soon forget it. She can still be a decent wife as long as she stops bitching, learns from this, and makes babies soon. Do this and the patriarch will be pleased.