Colleague abandoning resistance? Damn! (6)
I believe the answer is:
bother
'damn' is the definition.
(both are expressions of annoyance)
'colleague abandoning resistance?' is the wordplay.
'colleague' becomes 'brother' (brother can mean a colleague or fellow).
'abandoning' indicates named letters should be taken away.
'resistance?' becomes 'r' (electronics abbreviation).
'brother' with 'r' taken away is 'BOTHER'.
(Other definitions for bother that I've seen before include "Discommode, annoy" , "Irritate - concern oneself" , "Fuss and annoyance" , "Cause worry or annoyance" , "Annoy or pester" .)