In the interests of virtue, I'm getting impatient (3,8,4)
I believe the answer is:
for goodness sake
'i'm getting impatient' is the definition.
'in the interests of virtue' is the wordplay.
'in the' means one lot of letters goes inside another.
'interests of' becomes 'forsake' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'virtue' becomes 'goodness' (I've seen this before).
'forsake' going around 'goodness' is 'FOR GOODNESS SAKE'.
(Other definitions for for goodness sake that I've seen before include "Words of exasperation" , "Really!" , "please!" .)