we haven't discovered anything dangerously unfriendly... Or anything that can't be boxed.

Since many humans are difficult to box, I would have to disagree with you there.

And, obviously, not all humans are Friendly.

An intelligent, charismatic psychopath seems like they would fit both your criteria. And, of course, there is no shortage of them. We can only be thankful they are too rare relative to equivalent semi-Friendly intelligences, and too incompetent, to have done more damage than all the deaths and so on.