As a former barista, I know dealing with rude customers is part of the job. So when a customer was rude to this Starbucks barista, he probably forgot about it quickly and moved on to the next thing. Such is the service life.
But the woman who was rude to him couldn't let it go. In fact, she did some self-reflecting and realized her behavior towards the barista was wrong. Then she came back the next day to deliver this note, which the barista, who goes by the name Circle Addict on Reddit, posted on Imgur:
"A woman came through the drive through yesterday and got a little irritated with me because we didn't have drink carriers," he wrote. "Today, she came back and handed me this."