Sure Not 

an Aussie abbreviation for "Are you sure you don't?". Usually only used by people with a university degree and later stolen by extremely good looking people.

good looking person 1 '' do you want a beer?''
good looking person 2 '"no thanks mate"
good looking person 1 "sure not?"

or

Lawyer "want a piece of cake?"
good looking person "no it will ruin my good looks"
lawyer "sure not?"
good looking person "your not a good looking person"
lawyer "no but I'm a lawyer"
good looking person "oh ok"

Note:
Can also answer the question "Sure not?" by reversing the question, making the answer "Not Sure"

Sure Not by Walking In my Dreams October 11, 2016

for sure not 

for sure, but not

origin: Scotland, mid-21st century, St. Andrews

for sure, or for sure not?

will Carol buy us a puppy? fur sure not

for sure not by Rhorry July 1, 2008

im not sure actually 

What someone says when they don't want to answer a question because they don't want to reveal the embarrassing truth.

Scott: So Bill, when did you first have sex?
Bill: Im not sure actually. It was a long time ago.

im not sure actually by OilikProfessional December 14, 2009

Syafinaz Binte Zainal dance category audition with portfolio (?) / not sure 

Syafinaz Binte Zainal dance category audition with portfolio (?) / not sure

Syafinaz Binte Zainal dance category audition with portfolio (?) / not sure

Syafinaz Binte Zainal dance category audition with portfolio (?) / not sure by Handle100 August 6, 2023

Not sure if 

A popular meme, often tagged using the squinty eyed pic of Futurama Fry. Used to check if something really is x or not, in a humorously stupid way.

Not sure if trolling
Or just stupid.

Not sure if wet
Or just period.

Not sure if by Ceastra July 30, 2011

Not Sure 

From the movie, "Idiocracy". It is the name that the machine gave the main character, Private Joe Bauers when he was getting his UPC code tattooed on his arm. After that, he was called "Not Sure" throughout the movie.

Female Reporter: It started off boring and slow with Not Sure trying to bullshit everyone with a bunch of smart talk: 'Blah blah blah. You gotta believe me!' That part of the trial sucked! But then the Chief J. just went off. He said, 'Man, whatever! The guy's guilty as shit! We all know that.' And he sentenced his ass to one night of rehabilitation.

President Camacho: Number 1: We've got this guy Not Sure. Number 2: He's got a higher IQ than ANY MAN ALIVE. and Number 3: He's going to fix EVERYTHING.

Not Sure by Ingridd August 3, 2008

I'm not sure 

Alternative: "I don't know"

In conversation, when the person speaking to you wants you to feel like you're part of the conversation, but doesn't want to give you an opening. This conveniently allows the speaker to continue to ramble on about something trivial while the other person can only stand there and take it.

I'm not sure what your favorite movie is, but mine is Garden State, and this is why...

I'm not sure by jaykay84 August 29, 2009