hai i have found the following sentence in cambridge advanced learner's dictionary which is very contradictory pls explain<br/><br/><i>I'll be with you <b>in a </b>jiffy. </i><br/><br/><i>I've just got to fetch some books from upstairs - I <b>won't be a </b>jiffy (= I'll be very quick). </i><br/><br/><br/><br/>how can i won't be a jiffy mean i'll be very quick?