Jan van Speyk's Flag of the Netherlands

Origins
Jan van Speyk was a naval lieutenant in the Dutch army during the Belgian Revolution. Defying the Belgians order to lower his flag, he instead blew up his ships’ store of gunpowder, killing himself and the boarding Belgians along with most of his crew.

Effects
Saying "Dan liever de lucht in" causes gunpowder to form in the area directly surrounding the person. When they finish the sentence, all the gunpowder explodes, usually injuring or killing those nearby.