赤手空拳
(one's) bare hands
I killed the tiger with my bare hands.

 
作威作福；盛气凌人；颐指气使
lord it (over someone)
Since she got the highest mark in the final math exam, she has lorded it over the other students in her class as if she knew everything about math.

 
防患未然 (在萌芽时就将其消灭，或一开始时就加以制止)
nip (something) in the bud
There are a couple of things bothering me very much that I want to nip in the bud.

身强力壮；非常健康
(as) fit as a fiddle/flea
He was fit as a fiddle when he was at law college.

 
(尤指因缺乏社交技巧而) 局促不安；不自在的
ill at ease
He is always ill at ease at parties.

 
忍气吞声
swallow one's pride
I was forced to swallow my pride and apologize to my boss for his fault.

每况愈下
go downhill; go down the Swanee; go from bad to worse; on the slide; on the wane
I'm going to leave the country. Since the present government came into power, the whole situation of people's lives has been going down the Swanee.

附注："Swanee" 是美国一条河流的名称，因史蒂芬˙佛斯特 (Stephen Foster, 1825-1864) 1851年的民歌 "Old Folks at Home" (家乡老友 -- 有人译为「老乡亲」) 而出名，歌词开头是 "Way down upon the Swanee River"。

坐失良机
miss the boat
She missed the boat when she said no to that deal. It turned out to be worth millions.

言出必行；言行一致；说到做到
suit/fit the action to the word
He suited the action to the word and married her last year.

 
言多必失
the less said the better
It is best to say nothing at all when you are in an unfamiliar environment because "the less said the better."

 
言归于好 (尤指长期不和后)
bury the hatchet; make one's peace
John and his wife who went to court yesterday to fight about their marriage have decided to bury the hatchet.