@BaronBattleBread Neutrally speaking, its all about slang here.
Sure, in normal places a knob means the usual things like a handle or a twisty lever thing, but this is the Internet and anything goes. In a regular dictionary its cited as the last definition, and if you turn your eyes to urban dictionary, you find that knob is synonymous with a particular of the male anatomy, and its regularly used as such in other countries- from my personal experiance the British and the Irish use it quite alot.so yes, its easy enough to see how one would associate knobhead with dickhead.
because theyre interchangable in todays language flow.knob
näb/Submit
noun
noun: knob; plural noun: knobs
a rounded lump or ball, especially at the end or on the surface of something.
synonyms: lump, bump, protuberance, protrusion, bulge, swelling, knot, node, nodule, ball, boss
"the drake has a black bill with a knob at the base"
a handle on a door or drawer shaped like a ball.
synonyms: doorknob, handle, door handle
"she turned the knob on the door"
a rounded button for adjusting or controlling a machine.
synonyms: dial, button
"the knobs on the radio"
a small lump of a substance.
"add a knob of butter or margarine"
NORTH AMERICAN
a prominent round hill.
vulgar slang
a penis. <=====
This is why Urban Dictionary is complete horseshit. It has a lot of shit that makes no sense because for the love of God if one word has about 50 meanings then what the hell has Internet turned into? I never believe into anything what these dictionaries say because a lot of people write in them stuff that makes absolute no sense. So honestly I wouldn't take that as any explanation. To me a knob is a door handle and that's what it will always be.