I have never seen any evidence that another human being can literally steal your energy like siphoning gas from your tank, but that isn't to say it can't be done. More likely, the energy vampires we deal with every day are those who use our energy to do what they could otherwise do for themselves. And, if taken one step further, they do it primarily for their own entertainment, indulgence, and personal gain. At times they do it because they are lazy or ignorant or even incompetent. But they do it ruthlessly and without cessation.
Now, with all that said, I will add that in many cases they aren't even bad people intentionally. They are our friends and relatives, our family members and co-workers. Many times they don't even realize what they're doing. Sometimes (if one is fortunate) when it is pointed out to them, they will make an effort to stop. Other times, if the energy vampire is just habitually predisposed to be an EV, they will simply find other ways of continuing their behavior, transferring it from one person to the next as they are found out.
I have known a lot of energy vampires who are simply too lazy to think for themselves. If 10 people go to a dutch-treat dinner together, and at the end of the meal everyone is figuring out their part of the bill... the energy vampire is the one who stares off blankly into space and says to the person next to them, "Figure out how much I owe, would you?" Harmless enough, but it's this type of behavior that can become not only annoying but if carried through day after day, year after year, can actually begin to be a severe drain - using someone else's energy to "figure out" some problem (whether major or minor) which should logically be one's own personal responsibility. At the grocery store, the energy vampire is the one who stands off to the side and waits for friends or relatives to pick up his/her bags, and will occasionally even exacerbate or create some imaginary ailment to explain why this is necessary. In the work place, the energy vampire is the one who is always having to get help to finish his or her work on time... yet is never really seen to be doing a lot of work. The list is endless, and I'm sure most of us can identify a few EVs in our lives.
Once upon a time when I was doing a seminar, I was also working privately with a friend who was experiencing seemingly severe and inexplicable medical problems. This person had always seemed to be very strong, and had recently married a handsome prince who was a dream come true for her. But shortly after her marriage, her health began to deteriorate. She could no longer work. She could barely hold her head up, and no doctor could identify the problem, except to say "phantom nerve damage" from an accident several years previously.
As part of this seminar I was conducting, I had to be onstage on Saturday, sort of an emcee thing. The programming started, and I was about 2 minutes into the opening chit-chat and first introduction when another friend began motioning frantically for me to come to the edge of the stage. When I did, I was informed that "Mary" was having a major episode with her illness, had become paralyzed, and was asking for me.
Of course, being younger and far more naive, I excused myself from the stage, handed the microphone over to someone who had Zero Clue as to what to do, and literally ran down 2 flights of stairs to see what could be done for Mary. In the back of my head, I was slightly annoyed, however, because if this woman was legitimately paralyzed, why was she calling me instead of 911? But I went. Because at the time (~1985) I thought it was "the right thing to do".
At this time in my life, though I had had many strange occurrences and inexplicable insights, I could not say that I was a Seer - at least not on any official level. But immediately upon observing this scene, I "Saw" what was going on and I was not only appalled but outraged. Intuitively, I somehow "Knew" nothing was really wrong with Mary. Not. One. Thing. It was all in her head. Every. Last. Ache. It was as if the universe just downloaded that information straight into my brain. I Knew.
It looked real. It really looked real! And to this day I have no doubt that even Mary believed it was real. So. I stood there in the shadows of the stairwell for a few moments, took a deep breath, and decided to play the hunch, even though I had never done anything like this before. My association with "Mary" had been that of a good friend, personal healer, counselor, etc. I had done a lot of energy work with her regarding this ongoing, mysterious ailment, and my efforts had always been genuine, and offered from a foundation of unconditional love.
I walked up, managed to get through the crowds of Concerned Women who were cooing and offering much comfort, placed my hands firmly on Mary's neck, mumbled some nonsense incantation, then stepped back and watched without surprise as she sat up, blinked her eyes as if coming out of a stupor, and was miraculously healed right there on the spot in front of multiple witnesses.
I wanted to strangle her. But instead I turned and ran back up those 2 flights of stairs... and my friendship with Mary was never the same after that.
Point is, that night Mary knew I had obligations to others, and she devised a way (whether conscious or subconscious) to turn that energy onto herself. That is the nature of energy vampires, plain and simple, even when it might appear innocent. They find ways to focus your energy onto themselves, without any real Intent to change or grow as a result. Mary wasn't really cured that night. But the fact that she responded with a seemingly miraculous remission from her pain and her paralysis only revealed her true nature. It was a cry for attention, not really a plea for legitimate help. On the energetic level of Seeing, I knew that night that there was nothing really wrong with her... and her entire illness was only a means whereby to get her husband to become her caretaker and her friends to become her keepers. Was she aware of this? Doubtful.
There is no figuring out why some people make that choice. Doesn't matter. What matters in the warrior's world is the awareness that energy vampirism is very real, even when perpetrated by those we care about most. Had I allowed the cycle to continue, I have no doubt I would still be offering energy treatments and chakra alignments and crystal readings and all the other new age mumbo jumbo... all to no avail, because Mary didn't really Intend to ever heal herself. Not my place to understand why or even try to fix it. "Seeing" it is enough to bring about the realization that no shaman or medicine man or doctor or magician and "fix" what is not broken in the first place.
This isn't to say warriors are without compassion and love. Quite the opposite. It's one thing to give energy freely to those who take it and run with it and use it to begin creating their own evolution - for then it is no longer vampirism, but an actual energy exchange which brings growth and evolution to all concerned. There's a big difference.