It is a bad word and it said when someone ruins having your meal and turns it into unpleasant mean maybe by troubleing you or making you hear bad news which makes your mean ZAKNAPUT like a poisonous food.

It's an Iraqi dialect word here you can find a topic about it http://elsada.net/19426/ In general, it's mean like Nada said. As a Libyan this was the first time that I hear this word.