英语短语 "at one's expense" 是一个常用表达，核心含义围绕“由某人承担（代价/费用/嘲笑）”，具体意思需结合语境判断，主要有以下三类用法：
短语结构为 "at + 形容词性物主代词（my/your/his/her/their）/名词所有格（Tom's/Mary's） + expense"，本质是“以某人作为‘代价承受者’”。
表示“某笔开销由某人承担”，相当于“sb. pays for sth.”。
Let's go to the movies—at my expense!（咱们去看电影吧，我请客！）
The company sent him to training at its own expense.（公司出钱送他去培训。）
The dinner was at John's expense because he lost the bet.（晚饭由约翰付账，因为他打赌输了。）
强调“为了达成某目标而失去或损害某人的利益、健康、时间等”，常与 "at the expense of" 搭配（后接被牺牲的对象）。
His promotion came at the expense of his family life.（他的晋升是以牺牲家庭生活为代价的。）
We shouldn't develop the economy at the expense of the environment.（我们不应以牺牲环境为代价发展经济。）
She succeeded at her own expense—she worked 12 hours a day for years.（她的成功是靠自己牺牲得来的——她连续几年每天工作12小时。）
表示“以某人作为笑柄，让某人出丑”，常见搭配 "laugh/make fun/joke at sb.'s expense"。
The classmates were laughing at the new kid's expense because of his strange accent.（同学们因为新同学的奇怪口音而嘲笑他。）
Don't joke at her expense—she's already self-conscious about her height.（别拿她的身高开玩笑，她已经很在意了。）
The comedian's routine was full of jokes at the president's expense.（喜剧演员的节目全是拿总统开涮的笑话。）
"at one's expense" 聚焦“谁来承担”（人）；
"at the expense of" 聚焦“牺牲了什么”（物/事），后接名词/代词。
例如：
I paid for the trip at my expense = I paid for the trip myself.（我自己出钱旅行。）
I went on the trip at the expense of my savings.（我用存款的代价去旅行 = 旅行花光了我的存款。）
"at no expense"：免费（= free of charge）。
We got the samples at no expense.（我们免费拿到了样品。）
"spare no expense"：不惜代价（= spend as much as needed）。
They spared no expense for their daughter's wedding.（他们为女儿的婚礼不惜一切代价。）
总结来说，"at one's expense" 是一个灵活的短语，关键看语境中的“代价类型”——是钱、是牺牲，还是被嘲笑。通过例子理解会更直观！