"They're an easy, convenient way to show the world that you're a superficial, low-functioning douchebag* with way too much money."
Perhaps it's a guilty pleasure, but somehow I don't think there are many things that give as much satisfaction as the delivery of a well-timed, devastating insult. William Shakespeare was a master of this, which explains the popularity on the web of Shakespearean Insult Generators (see some examples here, here, and here). And there are other web sites dedicated to generating random insults for those of us not quick enough of wit to generate them ourselves ... for instance, Insult-o-Matic (which allows you to customize for various types of insults depending on your mood and intended target), and Elizabethan Oaths, Curses, and Insults (similar to the Shakespearean insult generators, but more ornate and with a better interface). There is also this wonderful compilation from BuzzFeed of 21 Scathingly Witty Insults by Famous People, which includes some of my personal favorites:
"His mother should have thrown him away and kept the stork" (Mae West);
"In order to avoid being called a flirt, she always yielded easily" (Charles, Count Talleyrand);
"He has no enemies, but is intensely disliked by his friends" (Oscar Wilde); and,
"He has all of the virtues I dislike and none of the vices I admire." (Winston Churchill)
Of course, one must be careful with insults, lest one be kinetically challenged by someone who does not appreciate your blinding wit. Since, thanks to the tireless efforts of the NRA, those someones are able to pack plenty of iron, this is not a trivial concern.
Do your worst, thou churlish sour-faced moldwarp!
Have a good day. More - possibly less-insulting - thoughts tomorrow.
* And how did "douchebag" come to be considered a derogatory term? You can read a few possible explanations here.