black sheep (n.)

• backslider
• blemish
• degenerate
• impurity
• intruder
• lecher
• miscreant
• misfit
• mote
• oddball
• pervert
• pimp
• profligate
• recidivist
• recreant
• reprobate
• scapegrace
• sliver
• speck
• splinter
• stone
• trollop
• weed
• whore