Irritation? After tea, smile! (7)
I believe the answer is:
chagrin
'irritation?' is the definition.
(I've seen this before)
'after tea smile' is the wordplay.
'after' means one lot of letters go next to another.
'tea' becomes 'cha' (cha is a type of tea).
'smile' becomes 'grin' (grinning is a kind of smiling).
'cha' put next to 'grin' is 'CHAGRIN'.
(Other definitions for chagrin that I've seen before include "Feeling of vexation or embarrassment" , "Annoyance/shame at one's failure" , "Frustration at having failed" , "Feeling of annoyance and embarrassment" , "Annoy" .)