A psychic vampire uses a technique which works in the opposite direction than a psychic attack: instead of hurling psychic energy away, the psychic vampire tries to siphon it in from others.
The psychic vampire feels an emptiness inside, and instead of facing that emptiness such people try to cover it up by bloating their egos with the energies of others. Basically, the psychic vampire tries to live the life of others. The tools of a psychic vampire are manipulation and inducing of fear.
Between adults, the energy transfer involving the psychic vampire and the victim is usually consensual on some level. (Children can be most at risk, especially if the psychic vampire is one of the parents.)
Defending against a psychic vampire does not require much sophistication. Simply decline to participate, as you would with a polite request.
Although psychic vampires subconsciously rely on a psychic technique, they are a far cry from being psychic.