Chuck Yeager
"from JBM to JWH"
John Wesley Hardin was an outlaw, he may have even been the Fastest Gun in the West, which seems to be a problem discussed here on Meta
Ghost of Winterbash Past
"I live... AGAIN!"
This hat was given out last year, and apparently you can get him the exact same way as you did back then...
I See Your Point
"Earned ten of the most meaningless points on the 'Net"
This is the meta version of another, non-secret hat...
Before It Was Cool
"He ain't no drag"
Come here sister.....Papa's in the swing
He ain't too hip...about that new breed babe
He ain't no drag
Papa's got a brand new bag tag?
Eureka!
"Solve these riddles and it's yours"
This one seems to be awarded manually, allegedly
IG-88
"You may have to go to Puerto Vallarta, break the law and then fight extradition to get over this one."
IG-88 was one of the Bounty Hunters from Star Wars. Duane Chapman was a real bounty hunter who ended up arrested when pursuing a bounty.
I'm Not Listening
"Humpty Dumpty, or perfect in every way?"
Humpty Dumpty appears in Through the Looking Glass making mistakes in English and saying, "When I use a word it means just what I choose it to mean—neither more nor less.", and Mary Poppins is "practically perfect in every way". Perhaps this is for those who don't take well to constructive criticism in some way?
Johnny Three-Hats
"You look like an absolute idiot"
Johnny Two-hats looked like an idiot, but if you collect more hats than him fast enough, you can be the idiot king.
Don Draper
"There are only so many people capable of putting together words that stir and move and sing. When it became possible to earn a very good living in advertising by exercising this capability, lyric poetry was left to untalented screwballs who had to shriek for attention and compete by eccentricity."
Hint: advertising
With Great Power...
"...then I took an arrow to the knee."
This is a meme from the Skyrim game where a character says, "I used to be an adventurer like you, then I took an arrow to the knee". My guess is that this may be related to the Great Power badge, since those who have it used to be users just like us, but then they took an arrow diamond to the knee.