Food "Service"

Okay, so I worked at a restaurant for almost 20 years. I have tried to make it a point to show patience at other restaurants, and I am usually good to waiters/waitresses. I also make it a point to not brag about my own experience when I do have a problem that needs to be solved.
Here's an experience that broke the deal with me and Wendy's:

I went for lunch, and ordered a combo meal, even told her to "biggie size" it without her asking, told her my drink flavor w/o being asked..I like to make it easy when possible-I know what they go through. When I got to the window, she looked at the back of my truck (not me) and said "six-fitty." I apologized, and said very nicely "I would actually like to add one of those yogurt things" (its what I really said). Her reply was "you can't add stuff at the window, six-fitty." Her manager was standing near her, and looked over when the girl said that. I asked the manager if that was true, that Wendy's doesn't want to increase their sales because its "at the window". The manager walked away without answering me. Now, as the reader, you may wonder if she didn't hear me..but I can tell you that she did. She, unlike the cashier, made eye-contact with me when I spoke, and turned after I finished my question.
Wendy's was never my favorite, but they were better than BK...now they are on the same level for me. I haven't been to BK in at least 5 years. This was bad customer relations, poor service, and poor business. My next visit to Wendy's will not happen for a looooooong time.