Porteño Spanish is the dialect of caste-sha-no (castellano) spoken in Buenos Aires, Argentina and the surrounding areas. It is categorized by an Italian-like pronunciation and colorful Lunfardo slang.Browse Slang Dictionary
to take a shit
"Garcar" has two different etymological origins, one more likely than the other. The first and more likely is that it comes from the syllable inversion of "cagar" which also means "to shit".
The other less likely origin is that it comes from the world "oligarchia" (oligarchy). These rich and powerful people would "shit" on the common people.