I remember learning in grade school about Euclid’s notion of transitivity: if A equals B, and B equals C, then A equals C. The same principle does not hold in language: a sausage is a banger, and a banger is a gang member, but a gang member is not a sausage. Be that as it may, sausages came to be known as bangers in the early twentieth century probably because a big, tight sausage can make quite a bang if it bursts its casing while being fried. For similar reasons, the word banger was also applied in the twentieth century to certain kinds of fireworks, to backfiring jalopies, and to especially noisy kisses. The gang member sense of banger, however, developed in a more indirect manner. First, the term gangbang arose in the 1940s to denote a sex act in which several men have sex with one woman. Next, the term developed a secondary sense in the 1960s, as it came to denote a streetfight between gangs, one in which heads get banged and pounded. Finally, the streetfighters came to be known as gangbangers, which was later, in the 1980s, shortened to just bangers. As for the word bang itself, it first appeared in English in the mid sixteenth century, though it had probably entered a northern dialect of English much earlier, perhaps from a Scandinavian source.