[corvallis]

1) I don't like feeling manipulated, regardless of if I am able to get over it. It's still a negative experience.

2) I belong to an ethnic minority that stereotypically does not tip well (though I don't see this in practice with others of my ethnic group). I don't want any judgment of me or my ethnic group based on if the person handing me my donut figures out, either by looking or by watching my hand motions, whether I tipped.

3) I don't doubt your description of the interface. I experience a similar interface. If I have to be prompted for a tip, then have to decline, then feel manipulated and have to expend mental energy to "get over it" (as you say), have to think about how I'm representing my ethnic group, and contemplate my role in the socioeconomic inequality present between myself and the people in the service industry (as mentioned elsewhere in these comments), well then I'm going to reduce that to a 2 step process where I hand over cash and receive my purchase.