The Double Down. The Waffle Taco. The Pizza Cake. Love them or hate them, these weird fast food menu items are taking over chains and dominating social media.

Judging by the last week alone, it seems fast-food chains are in a fierce competition to see who can outdo the rest in terms of freaky food items. First, Domino's introduced Specialty Chicken, which swapped out pizza dough with fried chicken as the base for pizza toppings. KFC countered with the one-two punch of the prom-ready Chicken Corsage and the return of the calorie-clogging Double Down. Then, word spread that Canadian chain Boston Pizza had entered the wacky food ring with a Pizza Cake concept, in addition to the Pizza Tacos and Pizzaburger sliders already on its menu.

While many scoff at the wacky mashups and outlandish concepts, there is a reason why fast-food chains continue to brainstorm the quirkiest things: social media. A freaky food item is bound to spread across Twitter and Facebook like wildfire, giving fast-food companies a chance to garner the attention of the highly sought-after millennial market. There's more innovation in the world of fast-food franchises than ever – and that's a good thing. 

The Double Down

Image credit: Michael Saechang

KFC's Double Down was one of the first fast food items to go truly viral online. The "sandwich" of cheese and bacon between two pieces of fried chicken was the subject of many a Youtube video when it launched in 2010. It even made an appearance on The Colbert Report, with Stephen Colbert calling a "warped creation of a syphilitic brain." And, this week, KFC announcedit would be bringing it back as a limited time offering.

Related: KFC to Bring Back the Infamous Double Down

Doritos Locos Tacos

Before the Cronut and the Waffle Taco, Doritos Locos was the freshest mashup in the food world when it was released in 2012. Taco Bell released sold more than a billion Doritos Locos Tacos in the first year it was available. The chain recently unveiled the latest flavor – Spicy Chicken Cool Ranch – over Snapchat, to be available for a limited time starting May 1. 

The McRib

Image credit: www.mcdonalds.com

By far the oldest item on this list, no discussion of weird, fast food cult-favorites is complete without a mention of the McRib. The boneless pork patty molded into a rib-like shape, slathered in BBQ sauce and topped with pickle and onion, made its debut in 1982. With farewell tours and support of a fan-made McRib locator, the chain has embraced the sandwich's difficult to obtain, cult-appeal, as part of its charm.

Related: For McRib Fans, Search for the Sandwich Is Worth the Effort

Bacon Shake

In 2012, Jack in the Box decided to combine two All-American favorites in a bacon milkshake. While the fast-food chain no longer offers the mashup shake according to their website, you can now fulfill your bacon milkshake cravings at Sonic, with the Peanut Butter & Bacon Shake

Waffle Taco

Taco Bell jumpstarted the quirky food trend in 2014 withbreakfast roll out in March. The chain's first foray into breakfast offered items including breakfast burritos and AM Crunchwraps, but what grabbed the public's attention was the Waffle Taco.

"I'd rather have people have an opinion than no opinion. I don't want to be in the land of same-ness," Taco Bell President Brian Niccol told Entrepreneur.com regarding the launch. "I'd rather be in the land of, you either love it, or you can tell me why you don't love it. What I don't want is bland."

Related: The Real Reason Taco Bell Made the Waffle Taco

Chicken Corsage

Image credit: www.kfc.com

Calling KFC's Chicken Corsage a fast-food innovation is a bit of a stretch, seeing as it's just a classic drumstick attached to baby's breath flowers and a ribbon. However, as the chicken-chain's commercial for the product hit 645,000 views on Youtube in one week, it is certainly getting the attention of chicken hungry high schoolers.

Related: KFC's Drumstick Corsages Are the Latest Quirky, Millennial-Targeted Fast-Food Experiment

Specialty Chicken

As chicken became an increasingly hot commodity in 2014, Domino's beefed offerings with the Specialty Chicken. The offering substitutes fried chicken for dough as the support for pizza toppings, with options including Crispy Bacon and Tomato, Spicy Jalapeno and Pineapple, Classic Hot Buffalo and Sweet BBQ Bacon.

Related: Long Seen as Boring, Chicken Is Becoming a Buzz Item for Restaurants

Pizza Cake

Image credit: Boston Pizza

Pizza Cake isn't on the market – yet. The mega-pizza is just one of the eight items competing in Boston Pizza's Pizza Game Changers campaign. The campaign, which launched on Monday, allows customers to vote online for their favorite innovative – or just plain bizarre – pizza products. In addition to the Pizza Cake, options include cheese clippers, pizza mints, a gas powered pizza cutter and a pizza protector guaranteed to keep hungry roommates away.

Related: Like It or Not, 'Pizza Cake' Could Soon Be a Thing