Evident eating a cold ham might do this (7)
I believe the answer is:
overact
'ham might do this' is the definition.
(ham can mean someone who overacts)
'evident eating a cold' is the wordplay.
'evident' becomes 'overt' (I've seen this before).
'eating' is an insertion indicator.
'cold' becomes 'c' (eg on taps).
'a'+'c'='ac'
'overt' going around 'ac' is 'OVERACT'.
(Other definitions for overact that I've seen before include "Play role exaggeratedly" , "In part, fail to convince" , "Be excessive on stage" , "Perform with exaggeration" , "Cartoon twenty four across" .)