The button won't close on me.
'Chiude' — 'KYU-de'. Two syllables. The 'chi' = 'ky' sound. Stress on first syllable.
When a shirt or jacket button can't close because the garment is too tight at that point. Specific feedback about a precise fit failure.
'Non mi si chiude' — reflexive + dative construction. 'Si chiude' = it closes (reflexive). 'Mi' = to me/on me. The full phrase 'non mi si chiude il bottone' is idiomatic Italian.
È troppo stretto sul petto.
It's too tight across the chest.
Describing the reason the button won't close
Fatico a chiuderlo.
I'm having trouble closing it.
More direct — I struggle to close it
Non si abbottona.
It won't button up.
Simpler reflexive form of the same problem
In Italian men's formal shirt sizing, collar size ('taglia colletto') is measured in centimetres and is separate from the chest size. This is standard in quality Italian shirtmakers like Borriello or Barba Napoli.