Which bone faces forward in your lower leg? The tibia, of course. How do you remember it? “Tits go in front.”
Such was the wisdom imparted to my dear spouse during emergency training for ski patrol while in college. The instructor allowed that it might be viewed as vulgar, “but you’ll never forget it.”
And neither of us ever has.
Not unique to me, but local:
Jesus Christ Made Seattle Under Protest
It’s the streets in downtown Seattle that run perpendicular to the waterfront, starting from the South end: Jefferson, James, Cherry, Columbia, Marion, Madison, Spring, Seneca, University, Union, Pike, Pine. A slightly odd mnemonic, since I don’t think Jesus had much to do with building the city, and it’s a pretty nice place - I don’t think He’d object to it.
One of my primary school teachers taught me this :
LATitude = horizontal
LONGitude = vertical
Think of the shape of your mouth during those syllables .
I remember this because “t” is higher in the alphabet than “m.”
For port and starboard, I remember port and left are lower in the alphabet than starboard and right.
When learning the Japanese phonetic system, I invented the mnemonic “Apples? I Usually Eat Oranges!” to help me remember the order of the vowels.
When we got to days of the week, I came up with “Nine Gay Knights Say ‘Men Kiss Delightfully!’” for Nichiyoobi (Sunday), Getsuyoobi (Monday), Kayoobi (Tuesday), Suiyoobi (Wednesday), Mokuyoobi (Thursday), Kinyoobi (Friday), and Doyoobi (Saturday). To avoid mixing up Kayoobi and Kinyoobi, I just had to remember that A comes before I (in both the Roman alphabet and the Japanese phonetic system, thankfully).
Not mine, but I learned “Do Men Ever Visit Boston?” from the book An Incomplete Education as a mnemonic for the ranks of the British peerage. From highest to lowest they are Duke, Marquess/Marquis, Earl, Viscount, Baron. This has come in handy more often than you might expect; not that I’m palling around with British nobility, but it’s useful to know who outranks whom in 19th century British literature (the reason it was included in An Incomplete Education), and now that Downton Abbey is so popular I’ve occasionally been asked where an Earl falls in the scheme of things.
Two.
First.
Mnemonic is the only word in the English Language that begins with M-N. I am not sure if it is true, but it was told to me in high school by a teacher and has allowed me to spell Mnemonic ever since.
Second.
To remember which side of the plate your bread plate belongs and which side your drink belongs, curl your thumb to your forefinger, holding the rest of your fingers straight. The hand that makes a lower case ‘b’ is the bread side and the side that makes the lower case ‘d’ is the drink side. It helps when you are at a large table in a fancy restaurant and you aren’t seated next to your wife.
excavating (for a mind)
This one probably isn’t unique either but I came up with it independently. Left, red, and port all have fewer letters than their opposite, right, green, and starboard.
i before e, except after c, or when sounding like A like neighbor and weigh… and neither. and foreign. and protein. and height…
I had to break myself of this because of faulty information. I was taught (by whom I forget) that stalagmites might fall on you and had to refute that with the dangling T and the built up M’s. Doubly slow because of double the mnemonics.
I like this one.
My feeble contribution: the joke: “What do you call meteors that miss the planet?”
meteor-wrongs
helps me remember that the ones in space are meteoroids, the ones mid flight are meteors, and the ones you can dig up out of the earth are meteorites.
A little one that I came up with: Dromedary camels have one hump, like a D, while Bactrian camels have two humps, like a B
Just a few months ago, I learned: Kings play chess on fine grained sand.
Another one I like:
Now, I have a rhyme assisting
My feeble brain its tasks resisting
(Digits of pi).
I see someone beat me to this, but I was going to mention these same finger configurations to figure our which drink glass or bread plate is mine at a set table. the lower case “b” is for bread, which is on the left; the lower case “d” is for drink, which is on the right.
Easier: just think of Chip’s chocolate chip nose. Dale is the other one.
Port & Left each have four letters. Stars are bright, which rhymes with right. Hence, port = left; star –> bright –> right.
In grade school I confused PEACE with PIECE. Until my teacher pointed out that PIECE includes the word PIE. A piece of pie. Mmmm. Pie.
For electrical engineering, our professor taught us “Eli the Ice man” as a way to remember that, with inductors (L), voltage (E) leads current (I) and that in capacitors ©, current leads voltage.
One I made up in organic chemistry:
Mary Eats Peanut Butter… Methyl, Ethyl, Propyl, Butyl… the rest I could remember no problem for some reason.
“and in words that are weird.” 
In geography class, it was hard to remember latitiude and longitude-which was the veritical and which the horizontal.
Then the teacher explained: latitude sounds like FATitude.
A big fat man has a belt around his middle. A line of "fat"itude is the belt line.
I like that one.
Onomatopoeia - the British English spelling - can be remembered by singing it to the tune of Old Macdonald Had A Farm.
i before e, except after c,
unless you want to run a feisty heist on a weird beige foreign neigbour…
I altered that to be “Camels often sit down mighty precariously…”
(And I learnt it as rusting, not rheumatism.)
To remember if you are heading in or out of a shipping channel say “red, right, return”. You have to travel between the red and green markers and they will always be on your right as you are returning from sea.
Blonde Women Really Are Fun
Buoyancy. Weights, Releases, Air, Final Check - The steps of a buddy check before a scuba dive.