不期而遇
I came across an old friend of mine in a department store. (chance to meet，bump into，come upon，meet...accidentally/unexpectedly/by chance/by accident)

不速之客
You are really a thick-skinned and gate-crasher.

不義之財(cái)
Don't be envious. Ill-gotten money comes easily and goes easily too.

不謀而合
see eye to eye：Do you see eye to eye with him on that plan?

不厭其煩
takes the trouble：The teacher often takes the trouble to instruct his pupils.

不遺余力
But the conspirators leave no avenue unexplored to re-establish contact with Britain.

不擇手段
by hook or by crook：He just did the work by hook or by crook.

不翼而飛
Did you see that plane? It seems that it just?vanished?from sight.

不聲不響
as quiet/silent/still as a mouse：She was as quiet/silent/still as a mouse and left.

不識(shí)抬舉
Bring a cow to the hall and she will run to the byre. (fail to appreciate sb's kindness/not know how to appreciate favor)

小Car筆記：

thick-skinned： 厚皮的，厚臉皮的，不敏感的

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