I got elastic pants, being swollen-headed (11)
I believe the answer is:
egotistical
'being swollen-headed' is the definition.
('egotistical' can be a synonym of 'swollen-headed')
'i got elastic pants' is the wordplay.
'pants' indicates an anagram (UK informal term for 'nonsense' or 'rubbish').
'i'+'got'+'elastic'='igotelastic'
'igotelastic' anagrammed gives 'EGOTISTICAL'.
(Other definitions for egotistical that I've seen before include "Excessively conceited" , "Selfish" , "Conceited and boastful" , "Highly self-absorbed" , "Self-important" .)