On thestudentroom.co.uk and other forums there are reputation systems in which users give points to other users for good or bad posts. Neg rep is when a person receives negative reputation, in contrast to positive reputation.
The people most likely to get 'negged' are trolls, general idiots, and people with opinions that others do not agree with, though some people will neg others just for the hell of it.
Negative reputation deducts points from the recipient's total reputation points shown by little green or red gems. How much rep you have decides how much rep power you have, which denotes how many points will be deducted from the recipient's power when you neg rep them. The more rep, the more power.
Some people believe that these gems represent how big their e-peni is, this however is not true -post count does.
New TSR user: Someone gave me neg rep :'(
TSR user: Shut the fuck up you whiney little bitch. I have so much positive rep! My E-Penis is HUGE!