I'm very upset with university's masculine element (6)
I believe the answer is:
osmium
'element' is the definition.
(osmium is a kind of element)
'i'm very upset with university's masculine' is the wordplay.
'very' becomes 'so' (both can mean 'extremely').
'upset' is a reversal indicator.
'with' means one lot of letters go next to another.
'university' becomes 'u' (abbreviation for university).
'masculine' becomes 'm'.
'im'+'so'='imso'
'imso' back-to-front is 'osmi'.
'osmi'+'u'+'m'='OSMIUM'
(Other definitions for osmium that I've seen before include "Lustrous, extremely hard member of the platinum metals group" , "Metallic element" , "Silvery-white metal, Os" , "Heaviest substance known" , "Densest of all naturally occurring metallic elements, Os" .)