act tough

Translations
вести себя жестко
She likes to act tough, but she's really very kind-hearted.
Ей нравится вести себя жестко, но на самом деле она очень добрая.
Definitions
To behave in a way that appears strong, brave, or intimidating, often to hide fear, insecurity, or vulnerability.
Words
act

verb
вести себя
tough

adverb
жёстко