Don't Drink From This Cup

I have been training Brazilian Jiu-Jitsu for a couple of years now and am a blue belt.  It has given me the unique ability to experience an injury that no one imagines....
I affectionately refer to it as cuphead.
Now, this may be too much for people that know nothing about Brazilian Jiu-Jitsu to handle so if this is you... stop now.
For those that are morbidly curious....
Brazilian Jiu-Jitsu is a grappling art like wrestling that relies on body contact and submission.
It is very common to get in some "unusual situations", one of which is a crotch on your head.  yes!  I said it.  Gross.  This is what I also refer to as a "motivating factor" to learn escapes.
Men often wear athletic cups to protect their junk... so to get to my point...
How do you explain to your child's teacher that the goose egg on the side of your head or the bruise in the middle of your forehead is a direct result of of... of....  ew... a... uh... um... uh....
Perhaps I should just say I took a ball to the head and leave it at that.
:)