clever Dick 
(also clever clogs)
noun British informal
A person who is irritatingly and ostentatiously knowledgeable or intelligent: she’s such a clever Dick—you can’t tell her anything...
- I would ban any clever clogs who has mastered either of those.
- ‘Because, clever clogs,’ explained the owner sagely, ‘before I put up the sign people kept tripping over him on the way in.’
- As we moved another furlong onward, I reflected that the clever clogs who first set the distance of the Blue Riband got it right.