Swaggering customer who’s on the pull at Christmas? (7)
I believe the answer is:
prancer
This clue is a double definition.
'swaggering customer' is the first definition.
(somebody who prances or swaggers around)
'who's on the pull at christmas?' is the second definition.
(one of the reindeer who pulls Santa's sleigh)
(Other definitions for prancer that I've seen before include "Xmas reindeer" , "A lively horse" , "Sleigh-puller" , "Spirited horse" , "One of Santa's reindeers" .)