Slang marks identity in social groups.
Belonging to a social group means knowing the language styles of the group and using them effectively.
However, slang usages tend to seep out from small groups to larger society.
Therefore, maintaining language barriers requires the constant invention of new usages. English, for example has at least 1,700 current and historical terms for sex.
Next: Code-switching
So, the cartoon above was funnier when I started using it. However, the fact that "pwned" has more or less disappeared proves a point: slang is constantly in motion. By the time someone like me is teaching it in a class, it's already gone. Here's an update:
But, of course, the fact that you're seeing it here means...
The 1700 words for sex reference comes from Jonathon Green: The Vulgar Tongue: Green's Dictionary of Slang. He also lists 1,351 for penis, 1,180 for vagina, 634 for anus or buttocks, and 540 for defecation and urination.
By the way, swear words change over time. Words that seem innocuous today were once considered terrible. Up until about 1800, almost all swear words in English had some kind of religious connotation. For example, there are lots of jokes about sex and defication in Shakespeare, but no one swears by them. They swear by religious things. Here's a fun list of the swearing in Shakespeare (though you might accuse me of having an odd idea of fun). By 1900, almost all English profanity was based on physical attributes and bodily functions, particularly sex and excretion. Many words that seem to us to stand for wholesomeness are actually "minced oaths;" that is, they are slightly changed obscenities. For example golly, criminy, and gee sound like something from a Hallmark special but all were blasphemies that have the same linguistic relation to God (or God's Body), Christ, and Jesus that frigging has to f**king. One of my favorites is "gee whiz." This shows up in the US in the 1870s. The origin seems to be the word "Jerusalem" (Matthew 5:35 specifically forbids swearing by Jerusalem, so of course it was a common swear word). Anyhow: Jerusalem-> Jewhilliken -> Gee willikins or Gee willikers, shortened to Gee Whiz.
Swear words also seem to have many different functions. One is that they help us endure pain. In a well known experiment, subjects were able to hold their hands in freezing water longer if they were permitted to swear while so doing. Why this works isn't clear but the evidence is that if you swear you will be able to do endurance tasks for longer than if you don't. So, my advice is that when you study for exams...