The word "dastardly" means to be cowardly or villainous. It is used to describe evil or despicable actions done by someone who lacks courage and shows a lack of honor or integrity.
Andrew and Jason were 8th - grade cousins, a dynamic duo of dastardly deeds, that fed off each other. (edutopia.org)
«So long as we are Nigerians, we can not live in isolation, but those who come to Enugu must respect out values and not engage in such dastardly act as we have witnessed recently.» (nigeriapoliticsonline.com)
That premise is also quite funny — we've seen lovebirds living together squabble to the point of dastardly deeds, most notably in The War of the Roses, and to some extent, Mr. and Mrs. Smith, but the angle that one of them is only pretending so that she can win the other back is an interesting wrinkle. (qwipster.net)