a zebra dick is a dick that has been so chafed by extreme gay sex that it takes on a striped appearance, often accompanied by pustulant leakage and/or open sores.

Someone's finger just didnt make it on the X and they typed ZD insted of XD

Abbreviation from the Croat nationalist slogan "Za Dom Spremni" (English: For The Homeland- Ready!) Heavily used by the Croat Ustasha Government in the 1940's and the Croat Home Guard during the 1990's Yugoslav wars.

Basically just 'Sieg Heil' for Croats online