Scifam
Colloquially, a backstabbing traitor or other such undesirable character. Can also be used to refer to an entire group of such persons (see examples)
Usage first arose on internet gaming sites. The exact origins are unknown, but the first part may be a conflation of the words 'sketch' and 'spy', thus referring to the unsavory information-gathering habits of someone who is scifam. The second half of the word, 'fam' may be a shortened form of 'family' thus indicating that unfortunately, there is a large number of people like this, as scifam prefer quantity over quality. 
"I just found out that the guy I thought was my friend completely backstabbed me"
"Dude, that sucks. But I always thought he might be scifam."

"This guys has, like, a couple hundred players following him, but they're all complete n00bs"
"Yeah, quantity over quality - typical scifam!"