Selfish activity got pier destroyed (3,4)
I believe the answer is:
ego trip
'selfish activity' is the definition.
(activity done for one's own ego)
'got pier destroyed' is the wordplay.
'destroyed' indicates an anagram.
'got'+'pier'='gotpier'
'gotpier' is an anagram of 'EGO-TRIP'.
(Other definitions for ego trip that I've seen before include "Something increasing one's self-importance" , "Self-centred journey?" , "Self-serving activity" , "Act of self-glorification" , "morale-boosting experience" .)