Remedy for a sore butt

We don't say boo-boo. We refer to body parts. It's the Montessori way, and I think boo-boo sounds ridiculous. I want my kid to say "My stomach hurts" or "I fell on my knee" not "I got a boo boo." And boys get hurt alot, so the Baboo knows all of his body parts.

A few weeks ago he was not looking where he was running (literally, his neck was at a 90 degree angle to the directional component of his velocity - it was a really strange sight, and you should try it sometime when you're in an open field) and he ran right into the sofa. The side of his face impacted a rather soft part of the sofa, resulting in a pretty decent bounce (you could almost here the -boiiiiing-) and then he skidded backwards on his bottom like a NBA player seeking a call.

So I went over to pre-empt the [fake] crying and kiss his cheek. A quick kiss, then the Baboo quickly stood up and took a couple of steps. Mission accomplished, I thought, and I stood to get back to whatever I was doing.

"Butt," the Baboo said, putting his hands on his lower back/upper butt.

"Yes." I said, deciding at that very moment that would be the official name of that body part. "That is your butt."

"Butt," he said again.

"Yes." I wasn't even listening. Mentally, I was picking out his clothes. It was morning, and there's a million things to do in the morning before I can even brush my teeth.

"Kiss it."

My first reaction wasn't to laugh or be annoyed, it was - how do I get out of this? What's my REASON for not kissing the butt and how do I explain this in a way that doesn't make him think about toileting or worse yet, that there's something wrong with what he said, and why that might be, and what the difference is and I'm not ready for this-- "NO," I said, and I really meant No to the panic of thoughts in my head, but the Baboo took it as NO I am not going to kiss your butt, and I guess it wasn't hurting that much by then anyway, so he went off to play with his wooden train.