Acronyms, the linguistic mode of contemporary communication, are very useful and popular because of their economy in use. They replace long names of political parties, of international institutions like 'ONZ' (UNO), as well as technical terminology (DVD, PC); communication in www is fully based on acronyms. The article investigates a popular phenomenon in Polish colloquial language: 'reinterpretation' of well known acronyms of standard language. This linguistic 'subversion' consists in lexical substitution: the right words, which make a well known acronym, are replaced by other words (with the same initial letter). This way the well known standard acronyms gain a new signification, usually ironic, malicious, but at the same time humorous: 'MO' (Milicja Obywatelska) Citizens' Militia, in the new interpretation: 'MO' stands for 'Mozesz Oberwac (You Can Take a Beating). This word game was one of linguistic self-defence mechanisms against the totalitarian language and flourished in the times of communism in Poland. The main purpose of the 'reinterpretation' of acronyms in social dialects of students or teenagers is to augment the expressiveness and the comic effects of the message.