borrowed plumes
A showy display that is not truly one's own. I know you lied to me earlier, so quit adorning yourself with borrowed plumes and tell me what you really contributed to this event.
plume (oneself) on (something)
To pride oneself on something in a vain, boastful, or showy manner. He plumes himself on his business acumen, constantly talking about how many big sales he's pulled in and how much money he earns. But so much as challenge one of their worldviews with facts, and the aloof nonchalance these teenagers plume themselves on will crumple like tissue paper.
plume oneself
Congratulate oneself, boast, as in He plumed himself on his victory. This idiom transfers the bird's habit of dressing its feathers to human self-satisfaction. [First half of 1600s]
borrowed plumes
a pretentious display not rightly your own. This phrase refers to the fable of the jay which dressed itself in the peacock's feathers.