From LQWiki

To adger means to make a bonehead move with consequences that could have been foreseen with even slight mental effort. E.g., “He started removing files and promptly adgered the whole project”. Compare dumbass attack. The term is a mutation of nadger, and it might come from the name of an infamous tenured graduate student.

This article is based, in whole or in part, on entry or entries in the Jargon File.