أخت شرموطة (Ukht sharmouta)

"your sister's a whore / sister-fucker context"

Calling a man's sister a sharmouta (whore) — the sister-targeted equivalent of 'ibn el sharmouta' (which attacks through the mother). Targeting the sister is considered by many to be even more provocative because sisters are younger, present, and the man's active responsibility to protect. It's the insult most likely to trigger physical violence across the Arab world.