You may well ask!

(humorous) also Well may you ask! (humorous, formal)

something that you say when someone asks you about something which you think is strange, funny, or annoying 'Why is Timothy sitting in the kitchen with a saucepan balanced on top of his head?' 'You may well ask!' 'What happened to the money you gave Sharon to buy food?' 'Well may you ask! She says she lost it.'