10th base is simple. It comes after 9th base, which is anal sex whilst strangling the person, so therefore 10th base is simply death. However, You have the option to have sex with the dead body or just leave it.
"Hey mate, u won't believe it but I finally got there..10th base action last night"
"Omg, trevor, I was joking. You just killed someone"
When you get to home base twice in one evening, then have a threesome with said two previous people.
Danny seduced two separate chicks, man! Then got to play with them together! Holy crap, he's the first in our college to get to 10th base! We must worship him.
A small piece of information. Derived from the word ken, used often in the scottish language and is synonymous with knowledge.
Person 1: "Hey I don't get this shit. How do you solve this problem?"
Person 2: "I got that one. Give me some kenlets on this assignment and I'll help you w/ that one."