R Gruppe is the most misunderstood car club out there. Rgruppe is early 911 car club. Treffen is their's annual meeting.
As Automobile magazine put it
R Gruppe is arguably the most exclusive, the most polarizing, and the most influential car club in the Porsche universe.
Read more: http://www.automobilemag.com/features/news/1008_bad_boy_porsches_r_gruppe_car_club/criteria.html#ixzz3BAXStjEA