كسمّين (Kussummein)

"double motherfucker / extra fuck your mother"

The dual form of kussummak — Arabic grammar has a specific dual number, and profanity speakers exploit it. 'Kussummein' theoretically references two mothers, which is biologically impossible but linguistically devastating. It's the Arabic love of grammatical escalation applied to the most common insult: if cursing one mother is bad, cursing two (via dual morphology) is worse.