Thanks for your opinions. I am glad my post inspired such a variety of topics. Let me add my thoughts, a day later.
I feel much calmer tonight, and I do not consider this a big deal any more, also due to what some of you wrote. I do not feel 'wronged' as much any more. I do not agree with a University cafe serving an unbalanced meal and operating in such a business-like manner. However, I did what I could and am willing to let go of this now. I believe I behaved respectfully in the cafe and the complaint email I wrote was brief, friendly, unemotional and constructive. I did not rant anywhere else, other than in this forum, where I finally let off the steam. Today I brought my own lunch again, which was much enjoyed.
Regarding the wording, the pricing in the cafe is price discrimination, in a marketing and economics sense. A 3-for-2 offer is price discrimination too. This is different from, say, discriminating against race or religion, and I did not mean to set these equal.
I was wrong when I wrote about illness above. Diabetes is a disease and I am actually very healthy. First, when I read the replies, I thought it is just wording, but it is not as simple. There have been many changes in my life, and I have been somewhat frustrated that the b***y diabetes is still there, although quite well managed during the last few weeks. I know that, mostly, I appear strong to others, and believe I have presented myself as strong in this forum in the past, but I am just human and the diabetes reminds me of the fact that I am not invincible. My usual approach is to bring my own lunch, seek out other options, pay more for my food, etc. etc. I am not sure what exactly triggered my emotional reaction yesterday. One thing I could have done, and was too proud to do was to be more honest and tell the serving lady that I was confused and wanted to have either some help or time to browse the available food options. Sometimes I need to remind myself that others might see a tall, athletic, slim (add any nice words here
) woman, when actually I feel small, insecure and vulnerable. It is then up to me to ask for what need or show some vulnerability, as appropriate. When I am then rejected, I need to live with it, but at least I tried.