Little Girl: "Mom, I have to go to the bathroom"
Mom: "Alright, as soon as we are done here"
Little Boy: "You can just go in the grass when we're done"
Little Girl: "Ewww, no"
Little Boy: "Why not?"
Mom: "Well, it's not so easy for us girls"
Okay, while true, how about adding a "Your father should never have taught you that. You need to go to the bathroom IN a bathroom".