A stoner is almost always a self given title, by people who smoke a lot of marijuana. These people tend to be non violent, yet extremely lazy. They do not contribute to society and spend most of their (or their parents) money on pot. Stoners are well known to be non constructive, apart from the odd one playing a musical instrument. Marijuana does not directly give them cancer or any extreme illness, but it does kill off creative braincells, despite what users may think. Some stoners have extreme short term memory and have selfish personality traits. A lot of stoners would pick pot over a lot more important things.
This is not a dig at stoners, this is what I have found out from my own personal research, at least 6 of my friends consider themselves as stoners, and this has been the basis for my definition.