I'm on fire可别理解成“我着火了” 老外会懵！

它就是on fire。

On fire这个短语的确有“着火”的意思。例如

The house was on fire for nearly an hour before the fire department finally arrived.

房子着火将近一个小时，消防队才赶来。

但是，在某些特定的场景中，on fire就不是它原本的意思了。尤其是表示某人的时候。

例如： He is one fire. 就前往不能理解为“他着火了”。

通常情况下，这种用法一般都用于文艺/体育活动中，表示“表现好”、“状态好”。

Performing very enthusiastically, adeptly, or successfully.

表现得非常热情、成功

例如：

The team has been on fire lately, winning 11 of its last 12 games.

这支队伍最近状态非常好，赢下了12场比赛中的11场。

除此之外，on fire还可以表示“灼烧感”

Having an intense burning sensation.

例如：

My legs are on fire after that workout!

运动之后，我的腿有一种灼烧感。

英语中，跟fire有关的常见俚语还有：

Fire off：

To make statements or ask questions in rapid succession.

快速密集地表达观点或提问

He fired off so many questions that I couldn't keep track of them all.

他快速地提出了好几个问题，让我有点招架不住。

Fire up：

To cause someone to feel more passionate or excited about someone or something.

使某人对某事产生更多激情

I know our players are nervous about the big game, but it's our job as coaches to fire them up.

我知道运动员们对这场比赛很紧张，但是作为教练，我的工作就是为大家打气。

Go through fire and water：

To face many challenges in the process of doing or accomplishing something.

做某事的过程中遇到种种挑战(相当于中文的“赴汤蹈火”、“历尽艰辛”)。

I feel like we had to go through fire and water to get here, since all of our flights were either delayed or canceled.

我们可能要历尽艰辛才能到那儿，因为所有的航班不是延误了就是取消了。

(There's) no smoke without fire.

There is usually truth behind a rumor, suspicion, or bad sign.

谣言、怀疑或凶兆的背后总有真实的成分(相当于中文的“无风不起浪”)。

I'm going to withdraw all my money from that bank. I read an article that the bank was in financial trouble, and where there's smoke there's fire.

我要把我银行里的钱都取出来。我读到一篇文章说银行现在有财政危机，无风不起浪。