Social circle incest, closely related to
dormcest, is, logically, the act of
dating and/or
sleeping with someone in the same
social group/
clique as you. Can be a
very good thing, or can be
living hell.
PROS:
SO already gets along with your friends so it's easier to go do group things with them. Your SO tends to already know your friends of the opposite sex, knows what they're like, and often is less jealous of the time spent with them, than random friends.
CONS:
Breaking up can destroy group of friends, cause people to take sides, etc, and be generally messy.