Snooty person rejected excellent little plant (6)
I believe the answer is:
bonsai
'little plant' is the definition.
(bonsai is a miniature tree)
'snooty person rejected excellent' is the wordplay.
'snooty person' becomes 'snob'.
'rejected' is a reversal indicator.
'excellent' becomes 'ai'.
'snob' backwards is 'bons'.
'bons'+'ai'='BONSAI'
(Other definitions for bonsai that I've seen before include "Japanese method of cultivating miniature trees" , "Dwarf tree found in Bosnia" , "Very little tree" , "Japanese craft of growing miniature trees" , "Mini-tree growing" .)