unbearable, intolerable
Roberto voleva restare ma la situazione era diventata insostenibile.
Roberto wanted to stay but the situation had become unsustainable.
Halloween is unbearable.
So che ciò ti mette in una posizione insostenibile.
I know that this puts you in an untenable position.
— La città proibita (2006)
Prego perché trovi un lavoro presto, la situazione economica sta diventando insostenibile per lui.
I pray he finds a job soon, the economic situation is becoming unsustainable for him.
The pain is unbearable.
Così, un'insostenibile gioia viene rovinata dall'attesa del risveglio.
Thus, an unbearable joy is ruined by the anticipation of waking up.
— Lo specchio (1975)
Seriously, you're impossible.
The smell is unbearable.