When a person of Alcoholics Anonymous has motives with another person (typically a newcomer) to take advantage of him/her for their personal gain. That advantage could be sex, financial or emotional. It often happens to newcomers who are open and trusting of the fellowship.
Someone or something that bites your ankles.
To a postman, an ankle biter is often known as a dog.
To an adult, an ankle biter may be a toddler.
To hikers, an ankle biter is sometimes a tick.
And so on.