Smarty-pants (8)
'smarty-pants' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for wiseacre that I've seen before include "Know-all" , "One claims to know all" , "Smart Aleck" , "One assuming air of superior wisdom - simpleton" , "Person who tries to appear clever" .)
(Other definitions for clever clogs that I've seen before include "Wise guy" , "Know-all" , "Smartypants" , "Smarties" , "Smart alec" .)