He was joking.
You must understand, Maxi, that we like to frolic in sarcasm land. And about your sister's friend, that's just f*cked up. My mom would pass out instantly if she heard that instantly, and I'm sure your moms the same. My mom health is no laughing matter and she needs to know that.
I'd definitely smack the bitch, no questions asked; or at least, force my sister not to hangout with her.