a soft giggle
A soft giggle is like a laugh that’s trying to be cool but fails. It's like a laugh that's too quiet for anyone to care.
He did a soft giggle when I said my dog ran away. It was too weak to be funny.
She did a soft giggle when I told her I could fly. She didn’t believe me.
I did a soft giggle when I saw my dog wearing sunglasses. I was too embarrassed.