Smile, looking embarrassed, showing up tooth (7)
'tooth' is the definition.
(grinder is a kind of tooth)
'smile looking embarrassed showing up' is the wordplay.
'smile' becomes 'grin' (synonyms).
'looking embarrassed' becomes 'red' (I've seen this before).
'showing up' is a reversal indicator.
'red' back-to-front is 'der'.
(Other definitions for grinder that I've seen before include "Operator of 12 across", "Eg, pepper mill", "Molar tooth", "Molar; miller", "Mouth".)