Here it's "your mom", and it can be inserted into any reply
Boy, it's hot today
Your mom's hot.
Man, am I tired
Your mom's tired
I don't feel very good
Your mom doesn't feel good
Etc., etc., etc.
This is from the high school students mostly. Sometimes, I must say, they are very funny. But, not when it's said to something my daughter says, and I am right there. Sometimes it's not very flattering, even if they don't mean it.