Horn effect

Etymology

The negative twin of the halo effect, which Edward Thorndike documented in 1920 when officers who rated a soldier well on one quality rated him well on all. The "horn" (or "devil’s horns") label flips the angel’s halo image: one bad mark casts a shadow the same way one good one casts a glow.

noun · /HORN ih-FEKT/
The tendency to let one negative trait darken your whole impression of a person or thing.
What it names
How a single off-putting detail — a typo, a limp handshake — can taint everything else, whether or not it’s relevant.
Example
A typo on page one triggered the horn effect, and the reviewer read the rest of the résumé looking for faults.
Related idea
Halo effect is the flattering version of the same machinery; the horn effect is what happens when the first impression is bad.