To advance one's own agenda, career, reputation, etc. at the expense of another person or group, specifically by criticizing, tearing down, embarrassing, or belittling that person or group. Such behavior is in lieu of advancing one's own agenda, career, reputation, etc. solely on the merits of such.
We've all seen people in the office who like to negavance into job promotions or sweet assignments -- they usually leave a trail of bodies.