An adrenaline junkie is somebody who feels as if they are addicted to adrenaline. Adrenaline junkies may enjoy competing in extreme sports like skydiving, surfing, mountain biking. They may also fuel their addiction by choosing to endure such experiences as riding on theme park rides, or getting tattoos or piercings, or anything else that gets their heart rate up. This sort of addiction is brought on by enjoying the (adrenaline) "rush" gained from these activities.