"I want to remove a mare's potty training. Leave her with the knowledge of what one is, and the knowledge that she used to have it and is now missing it. Let her understand that other ponies use the potty, but a block in her mind completely skips the concept of herself being able to use it. "

>Be a pony
>Spending time with your friend
>Things are kinda awkward, better to deal with this now
"Ok, that's it, I have to ask. Why the buck are you wearing a diaper?"
>"What do you mean?"
"Did something happen? Did you get hurt? Are you sick?"
>"No? Why would I be? I'm touched you care, but you're being kind of weird today."
>This mare is just gonna act like this is normal?
"Ok, then why in the name of the sisters are you trotting around in a... Wait, did you just piss yourself?"
>She absolutely just did! Huge yellowed spot, she needs to drink more water.
>"Well what else was I supposed to do?"
>Your brain is trying its hardest to not pop any blood vessels.
"What do you-, Why would you not go to the bathroom?"
>"But I don't need a bath? I can clean up just fine with wipes during my change?"
>You are rapidly approaching the point where you should probably just shut up and accept this.
>You NEED answers at this point though. 
"You can like, feel when you need to go, right?"
>She nods.
"And you remember where the toilet is, and how it works?"
>She nods.
>"Well duh. Ponies relieve themselves in it."
"So why wouldn't you go use it?!"
>"What do you mean, use the toilet? Use it for what?"
"Buck it, just don't leak on my furniture."
>You need some less weird friends.