Dar mole- in that special case, obviously.
One would have to translate "dar mole" in English in a case-by-case basis, since "dar mole" could mean a lot of things:
"deixar barato/vacilar/fazer M/deixar fácil para alguém/perder uma oportunidade que estava no papo/dar mole pro azar/dar chance pro azar/dar sopa/marcar touca/dar sopa pro azar...etc.
Let´s say the case a guy comes home and show this report card to his mother and she notices that he got a "B". Let´s say knows that hubby isn´t going to like this (even if she is a bit on the "soft side"), she would say "you really messed up this time uh? Your dad isn´t going to be much happy about this!
That would be one way (one of them) to express "você deu mole dessa vez hein?/você vacilou..."
A bit stronger would be "you really screwed up", even impolite sometimes.