Последняя капля переполняет чашу

Any endurance has a limit. See Всякому терпению приходит конец (B)

Cf: The cord breaks at the last but the weakest pull (Br.). It is the last feather that breaks the camel's back (Br.). The last drop makes the cup run over (Am., Br.). The last drop makes the cup turn over (Am.). The last drop wobbles; the cup flows over (Am.). The last ounce (straw) breaks the camel's back (Br.). The last straw will break the camel's back (Am.). When the pot's full, it runs over (Am.). When the pot's full it will boil over (Br.). When the well is full, it will run over (Br.)