(finance) Paid for by an individual or group.
(by extension, idiomatic) At one's responsibility.
(figuratively) In a way as to harm somebody or something; to the detriment of.
(figuratively, humorous) Making somebody seem foolish following a joke aimed at them.
Source: en.wiktionary.orgBe advised that all flatterers live at the expense of those who listen to them. Jean de La Fontaine
The state is the great fictitious entity by which everyone seeks to live at the expense of everyone else. Frédéric Bastiat
Raillery is a mode of speaking in favor of one's wit at the expense of one's better nature. Montesquieu
A sure way to lose happiness, I found, is to want it at the expense of everything else. Bette Davis
The price of a laugh is too high, if it is raised at the expense of another. Dutch Proverb
You can never be happy at the expense of the happiness of others. Chinese Proverb