(none original, but) these have been my go-to's recently ~
"it took me a long time to realize I was a slow learner"
"Thou wilt regret thine actions, swine!"
(I like to use this one when the one of the cats has been particularly destructive)
"Humala Bibuhla Zoobahla Bibuhla Humala Bibuhla Zoobahla bop"
(Probably my favourite ear-worm over the last few weeks)
and
Mrs Fogsbane is often wont to say, when I have forgotten about a chore she has asked to be completed -
"You have hidden yourself well"