"If you are on a company computer, prove they don't have a keylogger on it?"
Prove that your personal computer doesn't have one. Unless you've personally reviewed all the code and circuitry that could possibly be used for such a purpose, I shall not believe you.
"When the end cert is presented by an unknown party, it's a MITM."
It's a MITM when it's done by any party, known or unknown. If the data is being decrypted and captured as it flows between the endpoints of an HTTPS connection, the party doing so is a Man in the Middle.
"When it's done by the computer owner, under explicit ToS you agreed to, what's the complaint?"
Whatever the complaint, it involves the fact that "agree to" and "agree with" are different concepts.