Often, a chess player will find their knight attacked and move it forward to threaten the opponent’s pieces, only to find it trapped and unable to get out of the thicket. I called this an “Iraq knight”…no exit strategy.
Closely related is “do vajay,” the feeling you haven’t been, but you’re going to come soon.
“Pizza bones” for the crusts. Only it wasn’t me, it was my then toddler (who’s now 34).
“Maybe you oughta go sleep off some of that evil.” In a gaming session, with a rather immature gamer who’d decided he wanted to play an evil paladin. He went around being EEEEEEEVIL until the city guards caught him and threw him in jail, where he could, one hopes, sleep off… well, you get the point.
My 12 year old went through this phase a couple of years ago a well. She added an “L” to the “W”, “E”, and “M” for what ever major loser. It was annoying.
“Lemon”-The Asian equivalent of “white trash”
When my kids were toddlers, I used to tell them: “If it’s not yours, LEAVE IT ALONE.”
It got to the point where they knew the SAYING just fine, but the lesson just floated away…
~VOW
I love this one.
I don’t get it. 
Earbud pollution - the noise leaking out of the earphones of someone who’s listening to an iPod at a high volume.
*Shopping-mall osmosis *- When a popular song you’ve never purposely listened to sounds familiar to you, even though you’ve never consciously listened to it - you’ve heard it so often in the background at shopping malls, stores, etc. that you’ve picked up the song through shopping-mall osmosis.
I coined “wading in the shallow end of the gene pool,” back in the early '90s.
Also the word “shrugnostic,” meaning someone for whom the God question is irrelevant; someone who doesn’t care whether or not there’s a God.
Bumpdate - bumping an old thread to provide an update. I invented it to me but I may not have been the first.
Thanks we do too! Our family just loves family in-jokes and sayings. Once one gets coined, it’s family lore forever. 
My daughter is bright, so a lot of them come from her babyhood/toddlerhood.
I found the source of this.
From the Iliad:
Odysseus: Δεν είναι πυραύλων χειρουργική επέμβαση
See Jamais vu.
I invented the word disagrievance. I’m still waiting for it to catch on.
Yet somehow I heard it when I was in college in the 80s.
French Cake Palace - My name for the Cheesecake Factory. One day I was trying to tell a friend where to meet us and for the life of me I couldn’t remember the name, my brain substituted those words and it just stuck. Now that’s all I call it.
Mouth Ghost - When your mouth suddenly gets haunted by a phantom flavor of something you haven’t eaten recently - sometimes for a long time. Like when out of no where you get the flavor of onion rings.
When I was younger an annoying person was a gaper. “Oh my og , he is such a gaper”
A pretty girl was a box. “Wow! Jeff’s new girlfriend is a real box”
Or maybe I coined it in the 70s. 
A whole lot of other Dopers have heard it too.
mmm
My friends used to get together every Friday to play Texas Hold 'Em. This tradition grew pretty big pretty fast, to the point we would switch homes to host games. One time, at Katie’s house, we had 2 tables with 7 players at each table. As the game progressed, it came down to 3 players at one table. The last three players were all blonde women. As the rules of the game allow, they kept switching winning hands so that there was no progress being made, just moving chips around. The 3 ladies collectively decided to fold the game and split the pot rather than play to a winner.
All the men (who had all been beaten out) were aghast at this decision. This isn’t how Texas Hold 'Em is played.
The ladies all agreed that they would just rather share the money than play a futile game. I decided to call this Blonde Logic. Which instantly became “Blondgic”. The definition: Only a blonde can think this way and thinks it makes sense. Because this way of thinking doesn’t follow the rules and nobody else thinks it makes any sense other than a blonde. Or in this case, a trio of blondes.
I like to think that Blondgic is more relevant than most people think, and now that I have this word in my vernacular, I think it is used more often than most people think. But that’s just me. (Because you can never know what a blonde is thinking).