Unprovoked
To do something without cause or warning.
I wasn't even hungry. I just ate that whole pizza...unporovoked.
Unprovoked Denial
The unconscious tendency for a guilty or otherwise culpable individual to offer unsolicited excuses, explanations or clarifications out of interrogative context.
If someone explicitly states, "I'm perfectly normal" when there has been no preceding accusation to the contrary--that's an example of Unprovoked Denial...kinda like "No Collusion" or "No Obstruction".