Vega, who wears a dress size US 18 (NZ 22), said: "When I heard the nasty things the women said, I honestly wanted to cry. It really hurt my feelings.
"How could these grown women be so mean to someone they've never met, let alone talked to?
"Growing up a chubbier girl, I always got snide comments about my weight from people who, for some reason, think it's their business.
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"Things like this usually wouldn't bug me, but the fact that I didn't know these women, and they said this so rudely and loudly-so I could obviously hear it-was different than other times.
"But I swallowed the hurt and thought of the best possible thing I could do back to them that wasn't horrible, but that would trach them a lesson about respecting others.
"Hopefully this was a lesson in treating others kindly, and maybe a lesson in karma as well."
Vega said when she first entered the shop she overheard the women making loud and rude comments about the person at the front of the queue, who was taking a substantial amount of time deciding which cake to purchase.
She said staff at the bakery, which she does not want to name, overheard the woman's comments about her weight, and gave her additional chocolates and cookies free of charge in support.
Vega claims the clearly displeased older woman, and her friend, sneered at her as she made her purchase of 20 mega-sized cupcakes-each the size of three regular cupcakes.
But she got her final revenge on them as she walked out of the bakery.
Vega said: "I looked the pair straight in the eye and asked 'could you please open the door for me? My hands are a bit full.
"Reluctantly, one woman held the door open before following me outside.
"I think, if you have nothing nice to say, don't say anything at all. I am NOT sorry for taking all of the cupcakes."
Vega shared the spoils with her co-workers, friends and family over the Easter break, before posting the story to social media.
On Facebook, she wrote: "Tonight, I was really petty.
"I bought every damn cupcake. I spent $54 on cupcakes just to be a b***h."