Gyrating hip, thong covering one's best part? (4,5)
I believe the answer is:
high point
'best part?' is the definition.
(I've seen this before)
'gyrating hip thong covering one's' is the wordplay.
'gyrating' indicates anagramming the letters (letters dance or gyrate around).
'covering' means one lot of letters goes inside another.
'one' becomes 'I' (Roman numeral).
'hip'+'thong'='hipthong'
'hipthong' anagrammed gives 'highpont'.
'highpont' placed around 'i' is 'HIGH POINT'.
(Other definitions for high point that I've seen before include "Most successful time" , "memorable occasion" , "the best part?" , "The best bit" .)