Butterfingers' exclamation
I believe the answer is:
'butterfingers' exclamation' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oops that I've seen before include "Exclamation of surprise or apology when making mistake" , "I'm sorry" , "Exclamation on making a minor mistake" , "The sound of stupidity" , "Clumsy me!" .)