Passenger (usually male, usually young) unable to occupy a seat on a suburban commuter train without spreading his legs wide open (as though suffering from severely swollen testicles) and so encroaching on the adjacent seat.
I boarded the 18.23 train and moved to the quiet car only to find a grupnik sprawled across the last available seat
Reserved only for the worst of the worst. People labeled as such are worse than assholes, dumber than idiots, weirder than spergs, more annoying than Bieber, more heinous than villains, and more disgusting than public bathrooms. Most likely all of the above.
The security van appears in the infamous Grand Theft Auto III and Grand Theft Auto: Vice City video games. Apparently a take on the well-known financial entity called "Goldman Sachs", while it is also phonetically similar to "Group Sex", a sex-oriented pun indeed. Very Rockstar style.
A grown-up in the minority, finding themselves among younger people. Coined by Adrian Spies, writer of the Star Trek episode featuring a post-apocalyptic world where only teenagers survived.