Why do I care?

A female coworker of mine, P., has been getting coffee every morning from the shop on the corner ever since she started working here seven months ago. As people who frequent the same business tend to do, she has become acquainted with a few of the people who work there. She's a regular, and one guy in particular, J., who usually helps her, knows what she likes to drink. All she needs to do is go in, and J. sees her, knows what she'd like, confirms that she wants it, and he makes the drink for her. Often, when things aren't too rushed for either one of them, they will talk a little bit too: "How was your weekend?", "Have any big plans for this weekend?", "How's work going?", etc.

Within the past few weeks, J. has expressed an interest in P. She's uncomfortable with his interest, and has mentioned that she has a boyfriend to him. Still, he's becoming a bit more pushy and has started trying to suggest that they meet outside of the coffee shop sometime.

Last week, he wrote his name and phone number on the lid to her coffee before giving it to her, and winked at her, asking her to call him to arrange a time to go out. She was horrified and swore she would never go back to the coffee shop. Even though she enjoys the coffee, she's so upset by his pushiness that she doesn't feel comfortable returning to get her coffee there if he might be there. She has told him enough times that she has a boyfriend that it's overly aggressive of him to continue pushing her to see him.

I can't tell what I'm more upset about: his not respecting her boundaries, or her inability to get coffee if he's working there. I want to tell her to just go in there and tell him he's being a big jerk, because he deserves to have that feedback. I want to go in there myself and tell him to leave her alone, but it's not my place to do that and I don't want to reinforce her feelings of disempowerment. In fact, I have advised her to go in there and tell him to leave her alone, but she doesn't want to; she cites her shyness and unwillingness to engage in confrontation.

I support her right not to want to confront the guy, but it bothers me a lot that she is not going to do something she enjoys because she doesn't want to deal with an annoying person. It also bothers me that he's not going to learn that his behavior has caused her annoyance and discomfort.

The entire situation bothers me a lot more than it should, and I realize that I have more of a problem with it than even she does. So clearly, I have an internal trigger that this is nudging, causing me to become disproportionally upset. What that trigger is and why I have it: that's what I really need to figure out.