Origin

The gift basket of Exotic Butters is an item obtained on the fifth night of the fifth Five Nights at Freddy's game, Five Nights at Freddy's: Sister Location. Your robotic guide, the Model V Handyman's Robotics and Unit Repair System (usually shortened to HandUnit) awards you for completing your first week by giving you a gift basket. He then flips up a keypad to allow you to enter the kind of gift basket you want. As part of a running gag, the keypad fails and HandUnit "autocorrects" it to Exotic Butters.

If one were to complete the secret ending of the game and complete the fifth night, your Exotic Butters award will be laying on your television set as you watch the final episode of your favourite cartoon, The Immortal and the Restless. In the extras menu, the basket of Exotic Butters will be there. It will repeat HandUnit's out-loud autocorrection when left-clicked.

Spread

After Markplier finished the secret ending of Sister Location in his fifth playthrough video, he explored the extras menu. At the time code 17:25, he clicked the basket and laughed at the inevitability of its future spread as a meme, stating "How long until someone makes a remix of Exotic Butters?"
In response to Markiplier's challenge, several remixes have popped up of the phrase.

"an anthropomorphic bird" extracted the Extras Menu Exotic Butters image and sound and put it here.

Exotic Butters is used as a catchphrase.

Hey, I heard the FNaF movie's coming out.
HOLY EXOTIC BUTTERS!

..And at times referred to or replaced with "Erotic Butters." Exotic Butters is commonly used in conjunction with "Eggs Benedict" and "Casual Bongos" (rarely "Angsty Teen"), which are other autocorrections the game made for you (for your name, elevator music and companion voice respectively). It can also be the answer to a question to make it completely irrelevant. For example:

Q) What is your favorite food? A) Exotic Butters.
Q) What do you want for lunch? A) Exotic Butters.
Q) What should I name this? A) Exotic Butters.
Q) What do you want me to buy for you? A) Exotic Butters.

Urban Dictionary:
https://www.urbandictionary.com/define.php?term=Exotic+Butters&defid=10356266