This doesn’t really sound like a word for something heavy, does it? It might be the sound of a strange bird – a strange little bird – or perhaps a quick pluck on an odd stringed instrument, or some kind of a drip, maybe.
Yes, well. A strange bird, no doubt. A drip, oh yes. And little: the most common word to show up with twerp is certainly little. Other adjectives tend also to emphasize lightweightness – if not physically, then mentally or socially – and certainly lower status. And annoyingness, but usually the kind of annoyingness one envisions simply flicking off, like a burr off one’s sleeve, or shaking off like a self-important doglet on a leash. The annoyingness of the pesky little brother (I’m put in mind of National Lampoon’s January 1984 cover). An impertinence. As the Oxford English Dictionary puts it, “A despicable or objectionable person; an insignificant person, a nobody; a nincompoop.” Like a twit, but twit refers more specifically to intellectual lightweightness.
I think it’s reasonable to say a fair amount of the tone and flavour of the word comes from phonaesthetic influences. It really is a small, quickly chirping word, and one that causes the mouth to make a motion reminiscent of a dripping tap (say it, then again, then again). The etymology is opaque; although it has been asserted that it is from an Oxonian named T.W. Earp, last and most charming of the “decadents” and bane of the rugger set, this is not confirmed, and the Dictionary of American Slang gives a first reference as 1874, while T.W. Earp was at Oxford around 1911. And Earp, for his part, was president of the Oxford Union debating society, and a noted wit, so anyway not likely truly meriting the designation as we mean it today.
Between its appearance and now, a couple of fanciful stories have been confected, purporting to describe the exact sort of person a twerp is. One I heard (or read) when I was young was that a twerp was someone who bit fart bubbles in a bathtub. Kurt Vonnegut had another definition: “When I was in high school in Indianapolis 65 years ago, a Twerp was a guy who stuck a set of false teeth up his rear end and bit the buttons off the back seats of taxicabs. (And a Snarf was a guy who sniffed the seats of girls’ bicycles.)” (http://www.vonnegutweb.com/archives/arc_nice.html – he then goes on to apply it in a very non-literal sense to people who have failed to read certain works he considers essential.)
Well, and then there’s the question of exactly how we do mean it today. Aside from its “impertinent twit” sense, it’s also used to mean “someone who uses Twitter” – although there is still disagreement as to whether it applies to all users or certain types and whether it’s derogatory or neutral-toned. But ’twere pity to see a useful insult be bleached away…