Ariana: Miriam, what's that word that means crazy?

Miriam: Mishuga. Ari, you are a little meshuga sometimes.

Ariana: I know.

Rose: I'm meshuga with my Grandpa Joe and my Grandpa Jere.

David: Meshuga. Meshuga. Meshuga.

I don't know from Yiddish, and I need some help. What are the connotations for meshuga? Is it crazy in a fun silly way like the kids were meaning it or is it crazy like something you don't want in your life "those meshuga drivers, they keep running red lights."