She included a photograph of the barista, who was later identified as Lenin Gutierrez.
Public health officials now require Californians to wear masks or cloth face coverings in most settings outside the home.
Gutierrez asked her if she had a face mask and was about to show her the company and California's public health mandate of face masks, when Giles launched a tirade of abuse, or as Gutierrez said, "cursing up a storm".
Subsequently, however, Ms Gilles posted the picture she had taken of Mr Gutierrez on Facebook with the caption: "Meet lenen (sic) from Starbucks who refused to serve me cause I'm not wearing a mask". The customer then posted a photo of the barista and wrote a narrative of her visit, saying that next time she will bring a medical exemption to the place and will also call the cops.
The post has been shared thousands of times and racked up hundreds of thousands of comments.
The original post went viral with more than 133,000 comments and 49,000 shares before it was taken down Friday, and a GoFundMe campaign started on the barista's behalf has raised more $48,000 in "tips" for him, and it's steadily increasing.
A GoFundMe "tip jar" popped up in just hours, commending Gutierrez for standing his ground.
Amber attempted to get back at Lenin after he didn't serve her a drink by taking to Facebook and sharing a photo of him. However, there is a clause that says if a person has a health condition that prevents them from covering their face, they do not have to wear a mask. The state's outbreak is now second only to New York's.
There is now a GoFundMe campaign entitled "Tips for Lenin Standing Up To A San Diego Karen" with the sole goal of providing gratitude to the Starbuck's employee, Lenin, "for his honorable effort standing his ground when faced with a Karen in the wild".
"Everybody is rallying around somebody for doing what they're supposed to do and trying to protect everyone else", Cowan said in an interview with KGTV.
Gutierrez, an aspiring dancer, posted a Facebook video expressing gratitude for the donations, and relaying his surprise that an incident that lasted just a few minutes could result in something "so big".
"She started calling people sheep and she left".
"People don't ask you to do much, they ask you to wear a mask for your safety and the safety of others", Cowan told CNN.
While Gilles implied that she is medically exempt from wearing a mask, she didn't elaborate as to why. "The fact that now it went in excess of $65,000, I really don't know how to truly vocalize how grateful and blessed I feel with this possibility anyone has presented me". So from the base of my heart, thank you so a lot for it.
She said: "I am not scarred or bothered by your ignorant fraud ass's, not so sorry you losers got nothing better to do".