To take someones blood, specifically their red blood cells and inject it into your body. Increasing your own red blood cell count enabling you do be more active and go for longer. Blood doping is dangerous and illegal and shouldn't be done in athletics but happens anyway.
Blood doping on the streets is a real fun way of doing it. Get some poor victim, scare him, to get his adrenaline up, draw his blood, and insert it into your own body to get a natural high.
They wouldn't let me donate blood because I had been blood doping with so many different people. Aids for the win.