Make wrinkled, cold buttocks evenly sleek (7)
I believe the answer is:
crumple
'make wrinkled' is the definition.
(I've seen this before)
'cold buttocks evenly sleek' is the wordplay.
'cold' becomes 'c' (eg on taps).
'buttocks' becomes 'rump' (synonyms).
'evenly' means one should take alternating letters (the letters in even-numbered positions).
The alternating letters of 'sleek' are 'le'.
'c'+'rump'+'le'='CRUMPLE'
(Other definitions for crumple that I've seen before include "Become crushed" , "Pucker" , "Suddenly lose composure" , "Crush (paper)" , "Make wrinkled" .)