Mild sarcasm from fellow in City regularly (5)
I believe the answer is:
irony
'mild sarcasm' is the definition.
(I've seen this before)
'fellow in city regularly' is the wordplay.
'fellow' becomes 'ron' (masculine given name).
'in' indicates putting letters inside.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'city' are 'iy'.
'ron' placed inside 'iy' is 'IRONY'.
'from' acts as a link.
(Other definitions for irony that I've seen before include "Subtle humour" , "Use of words to imply the opposite of what they mean" , "Caustic remark" , "Gentle sarcasm" , "Kind of sarcasm, sounds metallic" .)