Conceit, for example, on top of obnoxiousness (3)
I believe the answer is:
ego
'conceit' is the definition.
(I've seen this before)
'example on top of obnoxiousness' is the wordplay.
'example' becomes 'eg'.
'on top of' indicates taking the first letters.
The first letter of 'obnoxiousness' is 'o'.
'eg'+'o'='EGO'
'for' acts as a link.
(Other definitions for ego that I've seen before include "Person's sense of self" , "Inner self" , "Conscious self" , "In Virgil I" , "One's sense of self-importance" .)