Hifalutin young boy leads girl (2-2-2)
I believe the answer is:
la-di-da
'hifalutin' is the definition.
('la-di-da' can be a synonym of 'hifalutin')
'young boy leads girl' is the wordplay.
'young boy' becomes 'lad' (I've seen this before).
'leads' is a charade indicator (letters next to each other).
'girl' becomes 'ida'.
'lad'+'ida'='LA-DI-DA'
(Other definitions for la-di-da that I've seen before include "Stuck-up" , "Informally, having affected manner of pronunciation" , "Hoity-toity" , "I'd a lad with affected manner or pronunciation" , "Affectedly genteel" .)