Ask him to explain years of medical knowledge?
Ok, I know this is a bit silly of a thing to say... But Medicine isn't THAT complicated.
I cannot think of any procedure that is so complicated, or condition so obfuscated, that a doctor couldn't explain both in a paragraph, maybe two at most.
"You have a cranial infarction causing the pressure in your head to increase. It will keep increasing until it crushes your brain. We will lower the pressure by drilling a hole into your head"
"But how do you know that I have this?"
"Well with the X-ray we took"
Would it be OT to have it happen here?
Executive summary: TBH I've found that even after dumbing down explanations people still ask for 'layman's terms'. One of the reasons why you think things are easy to explain is likely that you have dealt with people with a lot of experience in simplifying things down.
Sometimes even inter-speciality debate can get complicated.
One can get pretty terse with the explanation though. EG:
You hit your head.
You are not able to stand, or walk.
Your speech is slurred, and your eyes do not properly dilate when exposed to light.
These are all signs of either swelling or bleeding inside your skull.
We took X-Rays to determine which of those it was. The X-Ray shows bleeding. You can see it here, on the exposure.
You have a choice. You can either allow us to drill the relief hole, and allow the blood to escape from the inside of your skull before you go into a seizure, coma, or worse--- OR-- you can choose to risk having those bad things happen, along with possible long term brain injury.
Your choice.
Etc.
On the topic of the whole "Mansplaining" turdfest;
Shutting somebody down by playing the mansplaining card kills the second part of free speech-- that of other people to hear what is being said, and to join the conversation. It is extremely short sighted, and arrogant, to assert that your reaction to the person trying to give the explanation is the be-all, end-all of the discussion. If you choose not to participate in the discussion, there are better ways to extricate yourself than trying to shut the OTHER person down.
Additionally, the assertion itself-- that there is absolutely nothing this other person can say that will increase your understanding or knowledge, is a flat out fabrication created by the intellectually lazy. That is of course, unless you have perfect omniscience-- something I very much doubt.
The better way to go about this, is to say "I am finding this argument rather tedious, can we please not discuss this topic?" Not to basically say "I refuse to listen to anything you have to say, your boorish and unrelenting person! I obviously know much more about this subject than you do, and there is nothing you have to say that is of any value! I have given you the benefit of my wisdom, now away with you!" which is exactly what playing the mansplaining card does.