Put a fold in party clothes (3-3)
'put a fold in' is the definition.
(to dog-ear is to fold the corner of a page)
'party clothes' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'clothes' becomes 'gear' (I've seen this before).
(Other definitions for dog-ear that I've seen before include "Turned-over page corner", "Corner of a page turned down to mark your place", "Fold on page's corner", "Hint of shabbiness", "Crease in book page like canine appendage".)