underdressed
 US /ˌʌn.dɚˈdrest/
 UK /ˌʌn.dɚˈdrest/

1. 
malvestido, vestido de forma inadequada
wearing clothes that are too informal for a particular occasion
:
• 
I felt completely underdressed at the fancy restaurant.
Senti-me completamente malvestido no restaurante chique.
• 
She was worried she would be underdressed for the gala.
Ela estava preocupada que estaria malvestida para a gala.