how dare ...; how could ...
Expresses indignation or astonishment at someone's audacity. Often used in rhetorical questions or exclamations.
よくもそんなことが言えるね。
How dare you say such a thing!
よくもまあ、あんな嘘をついたものだ。
How could he tell such a lie!
Marks an outcome as contrary to expectation, often with a nuance of admiration or mild surprise. Less common than the indignant sense.
よくもこんなに早く終わらせたね。
You finished it surprisingly quickly.
How dare you say something so cruel!
It's surprising you managed to come all this way alone.