"Silly me!" (3)
(Other definitions for doh that I've seen before include "Tonic (mus.)" , "First note of major scale in music" , "an exclamation from someone who's annoyed with himself" , "for 7 [HOMER] of course!" , "The note C" .)
'silly me' is the definition.
(I've seen this in another clue)
This is all the clue.
(Another definition for duh that I've seen is " How slow".)
'silly me' is the definition.
(both might be said after making a mistake)
This is the entire clue.
(Other definitions for oops that I've seen before include "The sound of stupidity" , "Harem" , "Clumsy me!" , "Oh dear, that's a mistake!" , "I've made a mistake!" .)