Not in the slightest
Definition 1 of 1
Pro Tip 1/3Emphatic Negation
The phrase emphasizes strong denial of feeling, interest, or connection. 
She was not in the slightest moved by the movie.
Pro Tip 2/3Complete Indifference
It conveys total lack of concern or interest, often used to dismiss something as unimportant. 
He's not in the slightest worried about the exam.
Pro Tip 3/3Colloquial Usage
Used mainly in informal contexts like casual conversations rather than formal speech or writing. 
No, I'm not in the slightest offended by your joke.