Originating in Dublin, Ireland the word "cuntstab" can first be traced back to a very early Joe Duffy show(for those of you not familiar with Irish media, The Joe Duffy Show is an afternoon radio talk show, broadcasted on RTÉ Radio & hosted by one Joe Duffy. The show deals with events affecting the lives of "real Irish people"). Cuntstab, both a verb and an adjective has two meanings. As a verb, it is Dublin slang for both consensual and non-consensual sexual intercourse (1). As an adjective it is a derogatory term for a person of limited capabilities, usually the mentally or physically handicapped (2).
(1) "I cuntstabbed the slut" -- Translation -- "I had sexual intercourse with that woman of loose morals".
(2) "G'wan to fuck. Ye're nothing but a mouldy cuntstab" -- Translation -- "I don't believe you. Would you please vanish from my sight? You are the equivalent of having unprotected sex with a woman of loose morals who has many Sexually Transmitted Infections".