Nattering nabobs of negativity.*
More hair than wit.
Just a few of the insults I’ve seen and savored. What are your favorites? Clean enough for MPSIMS, of course! 
*Yes, I know. It’s still a good one. Safire actually wrote it as “negativism” but I think “negativity” has better cadence.
Who cut your hair? Stops 'em cold everytime!
Not widely used, but my personal favorite is “cheeselog”. Clean, yet satisfying to throw at people and animals. Try it!
I’m partial to knucklehead, it’s a relatively benign sort of insult that can be used in a variety of situations. Credit to sportswriter Mike Wilbon (Michael Wilbon - Wikipedia) for popularizing it.
I use knucklehead as well, only I got it from the Three Stooges before Michael Wilbon was born.
I like : “I see you are too tall for your hair and too short for your weight.”.
I’m partial to the portmanteaued Chump and Knucklehead into Chucklehead which is my go to, clean insult.
My father’s favorite was “hammerhead”.
Use your head for something else besides a hat rack.
A family I knew from Alaska used “motherbear” as a curse word, as in “I hate this motherbearin’ show.”
Doorknob and dipstick get used a lot in my family. I personally like chowderhead.
My daughter started to call extremely boring people “bran muffins”, which has been shortened to “bruffins”.
From Time Bandits: “How wonderful to be so mercifully free of the ravages of intelligence.”
OP is treading on dangerously thin ice! The Gormless Wienie is not to be trifled with!
My Daddy used to call people ‘numbnuts’…he called his sisters the ’ buffalo- butt twins’. He called my brother ‘hemorrhoid head’. I was ‘boo-boo’. He liked insulting nicknames.
How did he react when someone called HIM that kind of name?
You are (being) the hobgoblin of little minds.
Well, not too many people ever had the guts to call him a name other than ‘sir’. He was a Marine corps drill instructor so, no it wouldn’t have been prudent, if you valued your teeth!
My old man once called my brother a, “Hammer-headed Unscrewed Bird’s Eye”.
40 years later, it still makes me laugh till I cry! 
Ah, I see. Apologize if this offends you, but he sounds like a mean-spirited bully who got a sadistic kick out of abusing those weaker than him.
You summed him up perfectly. He was a well known bully. But on the other hand he would help the poor down trodden person. And, babies loved him. His was a paradox!
Proving that people are more than any two-dimensional description of them.
Does remind me of Archie Bunker’s favorite insult for his son-in-law: “meathead”.