None of them were meant to be funny. I don’t find gay stereotypes to be particularly humorous, and some can be hurtful. Some of the ones presented in this thread are the equivalent of “Gay as something inconsequential”.
Oh yeah, the fist thing. 
I once read a fanfiction in which a woman described a male friend as “so far in the closet he’s handing me my shoes.”
Sometimes I say “gay as a Gucci bag full of rainbows.” Not sure where I read it, but it sounded funny to me. I’ve also heard someone, probably my brother, call his friend something like “gayer than a gay guy at Gay Land on ‘gays get in free’ day.”
I heard somewhere “he’s so deep in the closet that he’s finding Christmas presents”.
Of course, there’s an obvious Narnia version of that one too.
Gay as AIDS. Think it’s a South Park or Team America reference, or some moronic equivalent.
Gay as a Whistle.
Someone on the boards (probably Sampiro) referred to Michelle Bachmann’s husband as “so gay he sneezes glitter.”
Sorta. Not really. It makes more sense to say, “Queer as a three-dollar bill.”
Gayer than the volleyball scene in Top Gun.
I stole that one from 30 Rock but it’s my go-to.
With Barbra Streisand’s “The Way We Were” playing in the background.
Patton Oswalt said it best…“Gayer than eight guys blowing nine guys.”
… as a tree full of chickadees.
Gay as a hee-hank. Naw, I’ve never heard it. I just like using the word.
His nickname isn’t Slim; it’s Slender.
I say, I say - that boy’s as queer as a two-bob watch
I’ve always been partial to the good old “queer as a three dollar bill.” My students do occasionally use “gayer than Glee.”
My brain supplies “…so deep in the closet he gave Mr. Tumnis a reacharound.”
No idea if I heard that somewhere or if it’s just so darn obvious.
Turkish delight.
My family’s go-to for superlatives was, “Xer than X McX, Xest man in the world.” I think it’s from Blackadder, or might just be home-grown weirdness.
So, Gayer than Gay McGay, I guess.
Let’s please keep talk of peophiles out of threads about homosexuality.
It was “so gay he farts glitter.” While I have stolen.