thinking money

showing good sense and/or remarkable cleverness. Inversely, if one shows poor judgment and/or lack of cleverness, they are "not thinking money."

Dave: "Hey, man, instead going to the bar to meet chicks, let's throw a house party and tell our friends to invite everyone they know!"

Ken: "NOW you're thinking money!"

-OR-

Dave: "Why haven't car companies invented hovercars yet?"

Ken: "Who knows, dude? They're obviously not thinking money."

Let me think about that and forget it quickly

A phrase you say to someone when you don't want to consider their suggestion seriously.
A phrase you say to someone when they have an egregious suggestion or opinion.

Can I guy your gaming chair for $5?

Let me think about that and forget it quickly.

There's me thinking

There's me thinking is a idiomatic phrase that for some reason wasn't here on urban dictionary before, and for some equally unknown reason isn't present on any other online dictionary as well. But i'm here to bring this problem to an end.
This is something of a set phrase comes out of one's mouth whenever one thinks that someone was true but is proven wrong by something he just saw/heard/learned.

Exemples:
1:- Friend one, a bodybuilder wannabe, is caught having MacDonalds.
friend two: Whoa, wtf? And there's me thinking you were on a diet, huh?
2: -A non-binary leftist is caught eating meat.
Friend of him: lol, and there's me thinking all leftists were vegetarian.
3: If you see someone getting famous using an idea you thought you were the only one that had thought of, you can say: There's me thinking i was original. lol

think brain think

The action you want to take when someone is very uneducated and doesn’t think.

“You know cami?” “The girl that faked her pregnancy?” “She’s so stupid.” “Think brain think!”

think brain think

When you know somebody that is so stupid you just want to hit them on the head to get their brain going.

I swear when I heard what cameo did I just wanted to her her in the head and shout think brain think at her.

Thinking problem

Being stupid, not thinking about stuff, or having difficulty understanding things.

I’m worried about Sofia meeting a stranger, cause she has a thinking problem.

What wasn't I thinking?

Whenever something is forgotten or unmentioned, misspoken or mistaken, use the phrase "What wasn't I thinking?"

Andrea forgot her friend's birthday. She called her and said, Happy Belated Birthday--- "What wasn't I thinking?"