It can also mean somebody who has not been a drinker, does not drink excessively, or at all, but frequently or often acts like an alcoholic in terms of behaviors. Not slurring words and stumbling, but the actual behaviors (for example, and this is a very short list, being a critical, controlling, manipulative ******* all of the time).
My daughter thinks I'm a dry drunk and nobody is more qualified to make that assessment than she is. It's why I added an AA meeting to my Alanon rotation. It is helping.
Take care,
Cyranoak