A vaguely one-dimensional character in a TV
show, book, movie, etc. who appears suddenly and by all rules of
plot cliches should die but doesn't, or is the only character to survive after all the main characters are dead.
See anticlimactic.
When Helen killed
Cutter, Captain Becker survived for no reason, proving his status as a pinkshirt.
When
Harry killed
Voldemort, he inherently turned all the remaining Death Eaters into pinkshirts.
Let's face it. Eight of the nine Ringwraiths are pinkshirts.