Caffeine and pettiness are a dangerous combination.

Two coffee-shop patrons in Australia are currently in the midst of a silly feud over which one is the store’s top customer — and one has permanently modified her body to prove it.

PIC: MAN WHO URINATED ALL OVER A PENNSYLVANIA STARBUCKS HAS BEEN IDENTIFIED, POLICE SAY

Fraser Harvey, a frequent patron of the Sensory Lab in Melbourne, kicked things off earlier this week by declaring himself “Customer of the Week” at the coffee shop.

“The cafe near work doesn’t have a loyalty program so I made one for them,” he wrote on Twitter, alongside a photo of the poster he plastered on the shop’s wall, recognizing himself for “Outstanding Purchasing of Coffee in This Store.”

Harvey, however, soon returned to see he had some competition from a mysterious patron who not only declared herself “Customer of the Week (Every Week),” but also publicized the announcement in a framed photo she placed on the wall.

“I go back in and am confronted by this horses---,” Harvey wrote on Twitter upon discovering the photo. “Another customer has tried to one-up me. They’ve just made a very unpowerful enemy.”

FOLLOW US ON FACEBOOK FOR MORE FOX LIFESTYLE NEWS

The feud only escalated from there, with Harvey presenting the store with a much larger framed version of his self-awarded “Customer of the Week” accolade. But the mystery woman too got creative, and instead installed a projector in the store, which projected her image across the entire wall.

CLICK HERE TO SIGN UP FOR OUR LIFESTYLE NEWSLETTER

Harvey then organized a Sensory Lab loyalty program — titled the “Fraser Harvey Memorial Coffee Loyalty Programme” — and even make “staff uniforms” for the baristas to wear, decorated with his own face.

On Friday however, the mystery woman — identified by The Guardian as Harriet Noall, another frequent patron who works just upstairs from the shop — took the feud to another level, getting an image of a Sensory Lab coffee cup tattooed on her ribs.

“I may have just lost,” Harvey tweeted. “She’s upped the game.”

Harvey may just be playing possum, as he already told The Guardian he has “measures in place should things escalate further.”

“I’m not sure how he is possibly going to one-up that [tattoo] but I know that he is going to give it a go,” Noall told the outlet in response. “I am waiting with bated breath."

CLICK HERE TO GET THE FOX NEWS APP

Harvey’s sister, too, warned that her brother isn’t going to give up so easily.

“What this woman doesn't know is that my brother is a man who impulsively tattooed Enya lyrics on his arm,” said Harvey’s sister Sarah on Twitter. “This likely won't phase him at all. Watch out Harriet, he's bluffing.”