Smile after tea shows exasperation (7)
I believe the answer is:
chagrin
'exasperation' is the definition.
(chagrin can mean exasperation or annoyance)
'smile after tea' is the wordplay.
'smile' becomes 'grin' (grinning is a kind of smiling).
'after' is a charade indicator (letters next to each other).
'tea' becomes 'cha' (cha is a type of tea).
'grin' put after 'cha' is 'CHAGRIN'.
'shows' is the link.
(Other definitions for chagrin that I've seen before include "Feeling of annoyance and embarrassment" , "anything but delight" , "Disappointment, exasperation" , "Arching with annoyance and embarrassment" , "Shame at one's failure" .)