The smog in north China has been particularly horrendous for the past few weeks. In some cities, the PM2.5 (particulate matter smaller than 2.5 micrograms) index is over 1000 micrograms per cubic meter, and in some places has even reached above 1400. The World Health Organization recommends 25 micrograms per cubic meter as the maximum safe level. This means that the PM2.5 index in many Chinese cities often reaches levels that are 40 or 50 times greater than those recommended by the WHO.
Given these dangerous conditions, people naturally want to complain and criticize, but in China you get in trouble when you complain and criticize. One way to release one's ire while hopefully avoiding arrest is to use satire, sarcasm, and irony (in addition to puns and romanization, which we have often documented on Language Log).
A current internet meme for deploring air pollution is wèi rénmín fúwù 喂人民服雾 ("smog the people"). This is obviously modeled on Mao Zedong's deathless slogan exhorting the Communist Party to "serve the people" (wèi rénmín fúwù 为人民服务), with which it is perfectly homophonous.
China Digital Times (CDT) has a nice article on this phrase, which has been in use for several years, but whose popularity waxes and wanes with the severity of the smog. This month it has been particularly evident on microblogs and other cyber platforms.
Mao's slogan was also the basis for another reproof against unsavory trends promoted by the government of the PRC, viz., wèi rénmínbì fúwù 為人民幣服務 ("serve the RMB [i.e., 'people's currency']"), which was wildly popular already well over a decade ago (see here for a collection of images).
Another set phrase that was distorted for the purpose of lamenting the horrible air pollution in north China is zìqiáng bùxī 自强不息 ("self-strengthening without ceasing"), which goes all the way back to the I ching / Yi jing (Book / Classic of Change[s]). Refashioned by clever netizens, it became zìqiáng bùxī 自强不吸 ("self-strengthening without breathing").
If you'd like to learn more about this type of subversive Chinese netspeak, I recommend taking a look at Decoding the Chinese Internet: A Glossary of Political Slang.