An energy vampire is someone whose presence drains the energy from you, leaving you anxious, or depressed, or lethargic.
Be it conflict, or dullness, or plain old stupidity, something about him sucks you dry.
There is never a valid reason to engage with an energy vampire.
If you want to win, you need 100% energy.
That means not even thinking about people that suck your energy.
Just stay away.