Negaholic

The member, Mary Benson, was a longtime member of the church whom Elaine, despite all efforts at charity, had never been able to warm up to, since she was a classic half-empty negaholic.

Source: wiktionary

Even so, those whom corporate trainer and management consultant Chérie Carter-Scott would call “negaholics” will take glum comfort in the news that some Americans seem to be tiring of the Pursuit of Wow.

Source: wiktionary

An example might be a negaholic at work who is not helping you achieve your dreams. You know what a negaholic is, don't you? They are like an alcoholic that can't drink without becoming intoxicated. A negaholic can't seem to speak without griping or complaining.

Source: wiktionary