This is repeatedly asked-about on etymological and other forums - sometimes out of genuine curiosity, sometimes as a troll - and usually gets replies asserting that it's some kind of sexual term (if sourced, coming from the unmoderated dustbin that is the Urban Dictionary - which carried no article on the term until it appeared on iCarly in February 2009). The reality is that was a made-up epithet: there's no such English slang. I can only assume the story spread on the gossip circuit out of the same perverse desire to drag down excessively naive/wholesome children's shows that gave rise to jokes about Muffin the Mule and the urban myths about Captain Pugwash.
However, the word "hobknocker" does exist: a look in Google Books - see here - shows it to be an evidently rare US term for a piledriver or jackhammer - i.e. a pneumatic drill, probably the same thing described as a "hobnocker" in this legal transcript. Etymological speculation about these things can easily be on the wrong track (again as with speculations about "Pugwash"); at Askville there's a discussion headed What does the slang word "hobknocker" actually mean? This goes into learned discussion about "hob" and "knocker" being terms for minor imps - true enough - while ignoring the variety of meanings of "hob" for hardware with some kind of metal business end:
hob. n 2On this basis, "a hobknocker" is simply descriptive: a device with a metal tip that knocks things.
[Origin obscure: perhaps more words than one. Cf. HUB.]
1. a. (Formerly also hub.) In a fire-place, the part of the casing having a surface level with the top of the grate.
1. b. One of the level supports on the top of a stove over which pots and pans, etc., are placed to be heated, etc.
2. A (rounded) peg or pin used as a mark or target in games; esp. one of the iron pins used in quoits.
3. (Also hub.) ‘A hardened, threaded spindle, by which a comb or chasing-tool may be cut’
4. The shoe of a sledge.
- Oxford English Dictionary, OED Online, 2nd edition, 1989
Returning to iCarly: admittedly I feel a slight twinge of sympathy with anyone's desire to subvert it. I may be reading too much into it, but I'm not at all keen on its overt pro-Americanism in having an approximately English character as a buffoon and hate figure. I also find the theme song, Leave It All to Me, outright creepy for its 'manifest destiny' flavour:
So wake up the members of my nationI forget who commented that there's quite a narrow line between inspirational and totalitarian lyrics in songs, but I think this is right on that line. I'd love to see a cover of Leave It All To Me by Laibach (the Slovenian group whose Geburt Einer Nation, to provocatively satirical effect, fits fascist imagery to the German translation of Queen's One Vision).
It's your time to be.