To "fool around" with a person or number of people who is/are part of the closely-knit group of friends one has in his/her life. This act is often seen as a taboo, as it is prone to adding a negatively dramatic twist in the social lives of the interrelated people in said socially interacting group.
"OMG!@! what a bitch!"
"Let's hate them!"
FRIENDCEST - Dating friends, dating your friends friends. You already like them... your friends already like them, so why not....... fuck it all up?"
"I'm friendcesting your ex, Michelle.."
-"no worries mate, i'm doing your sister."
Alt. spelling: frencest.
Friendcestuous. Adj. describing a group of friends who have all dated each other, each other's exes, and each other's family members or an individual in said group. A small dating pool, the equivalent of a small gene pool.
Me: She loves to commit friendcest.
You: Man, that crowd is like a soap opera. They've all hooked up in every possible combination.
Me: How friendcestuous.
Me: Be careful before you date him. I hear engages in frencest.