non-believer 

That really annoying phrase repeated in high-pitched tones; derived from that used-to-be-hilarious-but-is-just-getting-old-now video on YouTube. aka Charlie the Unicorn.

"Shun the non-believer, shunnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn-nuh"

non-believer by WhoWhatWhereWhenWhyBitches March 20, 2009

I can't believe it's not butter! 

The exact opposite of a butter face. A girl who has a great face but not a good body.

I diagnosed myself with I can't believe it's not butter! I so need to start working out!

I can't believe it's not butter! by Kaydaymuchluv81 December 1, 2011

believe dat whoad 

a saying recited after being in grand excitement about something ; a phrase shouted out loudly in order to reassure one self of having completed a great task ; telling a prison warden to "believe that"

I just banged my "ho" and gave her some good "D"... BELIEVE DAT WHOAD!!!!

believe dat whoad by mr attached May 5, 2009

IT'S A BONUS! BELIEVE IT! 

A phrase originating from the video game Naruto: Clash of Ninja 2. The second half of the phrase originates from the phrase Believe it!. Originally used on the extras menu, it is used as an over enthusiastic response for something that one would not consider a "bonus" at all.
It is commonly used as punchline in a joke involving someone about to receive or do something somewhat desirable (engage in intercourse, win a prize on a game show, make a purchase). The second person mentions something very undesirable in addition to the initial object/act. The first person indicates their displeasure, while the second exclaims the phrase.

1: Congratulations! You've won a brand new car!
2: OMFG! This is the greatest day of my life!
1: But you'll have to time to use that car, as you've won a trip to maximum security prison!
2: WHAT?!
1: IT'S A BONUS! BELIEVE IT!

IT'S A BONUS! BELIEVE IT! by Cube B September 1, 2007

Belieftard 

You know, those college kids that preach world peace? Yeah, those.

I just saw these belieftards talk about "flat earth".

Belieftard by God'sDaddypop October 3, 2017

Belieber 

A person who loves Justin Bieber and Masturbates to his music

Geoff Prentice: Have you heard Justin Biebers music?
Helen Schmidt: oh yea! I’m such a belieber!!! Are you?
Geoff Prentice: Definitely!!!!

Belieber by EMOG HOWLY May 7, 2019

Believe All Mammals

The reasoning that victim and perp have the same credibility.

Congressman Jones asked the public not to choose sides, but to believe all mammals.

Believe All Mammals by Miso Grumpy May 12, 2020