Term originated in Star Wars: the Old Republic where you got Dark Side and Light Side points as a result for your actions. The display screen for those was also very "in your face".
Since Dark Side points were often given for actions that were morally good, but went against the wishes or teachings of the Jedi Order, "Dark Side" as a pun started to be applied to IRL actions that were in any way advantegous or convenient to the person voicing them.
Person 1: "I can't be bothered to study anymore... I'll watch some TV."
Person 2: "DARK SIDE!!!!"
Person 1: "What a nice day! I think I'll get off work early and have an ice cream!"
Person 2: "DARK SIDE!!!"
Person 1: "For once, I didn't clean my apartment this weekened, but played 30 hours of video games!"
Person 2: "DAAAAAARK SIIIIIIDEEEE!!!!!!!!"
Much similar to east and west/ north and south side unwritten zoning laws among underprivledged/well armed african americans, the Dark Side is one of many locations that a Star Wars fanboy (or Jedi) may reside to seek out refuge from polar gangs (often known as the light side, or "rebels")
However, by claiming a title from any of these nerd zoning laws, one automatically delays the next time he/she/it will have sexual contact of any sort. Also, Dark side members take a massive karma loss, but may wear sith armor.
Tim joined the dark side, and is now an evil sith lord. Let us beat him up my fellow negroes.
Colloquial name for the housing commission side of Wyoming, NSW. Hotspot for crystal meth, domestic violence and hoodlum activity. Also known as the "Ghetto Side" or the "Shit Side".
Bring your crew over to the DarkSide and we'll rape you silly!
Someone who started life as the superhero kid who was in line with all the rules, then went a different route as they got older, still trying to keep everybody in line.
He/she went with the dark side as he/she got older, and tried to win people over for his/her dark side.