One might be smiling, feeling cold inside (8)
I believe the answer is:
emoticon
'one might be smiling' is the definition.
'feeling cold inside' is the wordplay.
'feeling' becomes 'emotion' (emotion is a kind of feeling).
'cold' becomes 'c' (eg on taps).
'inside' indicates putting letters inside.
'emotion' going around 'c' is 'EMOTICON'.
(Other definitions for emoticon that I've seen before include "Wordless expression" , "Mince too (anag.)" , "Representation of facial expression in e-messages" , "Textual symbol" , "Smiley characters" .)