よくも
善くも
yokumo

Adverb

1. how dare ...; how could ...

Usually Written in Kana
よくもかおをつぶしてくれたな。
yokumo kaō tsubushite kuretana.
You really made me lose face.
よくも彼女かのじょにそんなことがいえるものだ。
yokumo kanojoni sonna kotoga ieru monoda.
How dare you say such a thing to her!
Adverb

2. surprisingly; unexpectedly

Usually Written in Kana