You never know, it may spread everywhere! BTW I strongly advise that if you do contribute one you google it first. Great minds think alike and it’s astonishing how many seemingly original thoughts have already been thunk, so to speak!
Here’s my contribution. It didn’t turn up on a cursory google but do let me know if I missed it and it’s already out there.
“The Devil whispers in dog’s ears”
-Little Lumpy’s Almanac
As easy as a rich man sticking a needle in the eye of a camel.
Proverbs according to running coach
You’ve buttered your bread-- now you have to lie in it.
Thelma’s Words to Live by.
If you know what you’re doing, it’s not an adventure.
Ethilrist’s Law
Novelty Bobbles law of judicious swearing…always have a cunt up your sleeve
Quoted by aldiboronti:
On being asked if he would marry again aldiboronti said long ago, Marriage is a mistake a wise man makes only once and a very wise man not at all.
The corollary (coronary?) [courtesy National Lampoon]: A wise man marries his second wife first.
See a pin and pick it up and all day you’ll have … a pin.
A penny saved is hardly worth the effort.
You’re always in trouble if you have to hope someone wasn’t stupid.
Two wrongs don’t make a right, but three rights make a left.
-The Fable of Buster Brown
Ah, a fellow pin-head.
Or a chess player. 
Chronos’ Maxim: The smaller the set of people who will get a joke, the funnier it will be to those who do get it. Corollary: The funniest jokes are always inside jokes.
Necessity is the mother of strange bedfellows.
I first heard this on I’m Sorry I Haven’t a Clue c. 20 years ago. Can’t remember who it was - probably Graeme Garden. Even then it may not have been original. It is a good one though, I hope pointing this out doesn’t leave you feeling too… deflated :).
A rolling stone gathers no moss, but if you really need a clean stone, you can scrape off the moss without rolling it.
When presenting a particularly scrumptious dinner course, I like to wink to the person I’m serving and say, “And if this stays down, there’s plenty more”.
Maybe more of a non sequitur than an aphorism, though.
There is no problem so bad that it cannot be made worse through brute force and ignorance.
To control the classroom, control yourself. ~DSYoungEsq, “The Tao of Teaching”