Underminer n. : One who undermines.

Example:


Taxonomy
Underminer, The Best Friend, Casually, Your Life, escape, college, freshman year, secret ambition, unfortunate choice, grandpa, greeting card, bring out your best, tubby, hobbits, Kits, Neds, bird, yelena.

Defination from the web:
Underminer. The Best Friend Who Casually Destroys Your Life. You can't escape him. ... The first book to channel that insidious voice, The Underminer plumbs the depths of the modern American psyche – where a new kind of horror lurks. ...