I trust you implicitly

"I trust you implicitly"

This is a humorous statement often said by one of my co-workers.

The reason why it is a joke is that it may (or may not) originally be a true statement, but once he says it, it is from that point definitely false. The definition of implicit that he is using is: "implied though not plainly expressed". The reason why it is false is that he is stating unequivocally in the statement that he trusts the person, and also that he has not stated that thought in words.

There is another sense of the word "implicitly" that he could use to make this not a joke, but I have talked to him, and I know for a fact that he means the first definition given, so he is using this statement as a joke.

The reason why it is funny is that it is an innocuous lie that requires the listener to detect that it is in fact a lie. It would be mostly funny to English pedants.