Usage of the character 当

lit. if you tap a half-empty bottle it makes a sound (idiom)
fig. empty vessels make the most noise
one who has a little knowledge likes to show off, but one who is truly knowledgeable is modest

bǎfāngbiàndàngsuíbiàn

把方便当随便

[把方便當隨便]

to act unappreciatively in response to a kindness

dāngmiànluó,duìmiàngǔ

当面锣，对面鼓

[當面鑼，對面鼓]

lit. gong facing gong, drum opposite drum (idiom)
fig. to come together to thrash out the issue face to face

děngxiàobǎiwàndūndāngliàng

等效百万吨当量

[等效百萬噸當量]

equivalent megatonnage (EMT)

názhejīmáodànglìngjiàn

拿着鸡毛当令箭

[拿著雞毛當令箭]

to wave a chicken feather as a token of authority (idiom); to assume unwarranted authority on the basis of some pretext

hǎohànbùtídāngniányǒng

好汉不提当年勇

[好漢不提當年勇]

a real man doesn't boast about his past achievements (idiom)

hǎohànzuòshìhǎohàndāng

好汉做事好汉当

[好漢做事好漢當]

daring to act and courageous enough to take responsibility for it (idiom)
a true man has the courage to accept the consequences of his actions
the buck stops here

bùdāngjiābùzhīcháimǐguì

不当家不知柴米贵

[不當家不知柴米貴]

a person who doesn't manage a household would not be aware how expensive it is (idiom)

jìyǒujīnrìhébìdāngchū

既有今日何必当初

[既有今日何必當初]

see 早知今日何必當初／早知今日何必当初 (zǎozhījīnrìhébìdāngchū)

zǎozhījīnrìhébìdāngchū

早知今日何必当初

[早知今日何必當初]

if I (you, she, he...) had known it would come to this, I (you, she, he...) would not have acted thus (idiom)
to regret vainly one's past behavior

Yánwánghǎojiàn,xiǎoguǐnándāng

阎王好见，小鬼难当

[閻王好見，小鬼難當]

lit. standing in front of the King of Hell is easy, but smaller devils are difficult to deal with (idiom)

yǒufútóngxiǎng,yǒuhuòtóngdāng

有福同享，有祸同当

[有福同享，有禍同當]

To enjoy blessings and endure misfortune together (idiom); for better or for worse

shàngyīcìdàng,xuéyīcìguāi

上一次当，学一次乖

[上一次當，學一次乖]

to take sth as a lesson for next time (idiom)
once bitten, twice shy

yǒufútóngxiǎng,yǒunàntóngdāng

有福同享，有难同当

[有福同享，有難同當]

To enjoy blessings and endure misfortune together (idiom); for better or for worse

yīfū-dāngguān,wànfū-mòkāi

一夫当关，万夫莫开

[一夫當關，萬夫莫開]

(idiom) one man guarding the pass can prevent the passage of ten thousand

dāngyītiānhéshangzhuàngyītiānzhōng

当一天和尚撞一天钟

[當一天和尚撞一天鐘]

see 做一天和尚撞一天鐘／做一天和尚撞一天钟 (zuòyītiānhéshangzhuàngyītiānzhōng)

dāngjúzhěmí,pángguānzhěqīng

当局者迷，旁观者清

[當局者迷，旁觀者清]

(idiom) an outsider can see things more clearly or objectively than those involved

gēngdāngwènnú,zhīdāngfǎngbì

耕当问奴，织当访婢

[耕當問奴，織當訪婢]

if it's plowing ask the laborer, if it's weaving ask the maid (idiom); when managing a matter, consult the appropriate specialist

jìyàodāngbiǎoziyòuyàolìpáifāng

既要当婊子又要立牌坊

[既要當婊子又要立牌坊]

see 又想當婊子又想立牌坊／又想当婊子又想立牌坊 (yòuxiǎngdāngbiǎoziyòuxiǎnglìpáifāng)

yòuxiǎngdāngbiǎoziyòuxiǎnglìpáifāng

又想当婊子又想立牌坊

[又想當婊子又想立牌坊]

lit. to lead the life of a whore but still want a monument put up to one's chastity (idiom)
fig. to have bad intentions but still want a good reputation
to want to have one's cake and eat it too

dāngguānbùwèimínzuòzhǔbùrúhuíjiāmàihóngshǔ

当官不为民做主不如回家卖红薯

[當官不為民做主不如回家賣紅薯]

if an official does not put the people first, he might as well go home and sell sweet potatoes