Bartenders are special, they've always been traditionally tipped and also they also manage an informal queue. In cases where I'm tipping $20 (or more) up front

Bartenders are special, they've always been traditionally tipped and also they also manage an informal queue. In cases where I'm tipping $20 (or more) up front it's because it's busy and it's literally a bribe to put me at the front of the queue. Tip-as-a-bribe is socially useful to me and any job where I can effectively bribe for better service, I will. Coffee is marginal. The places in walking distance to my house get a tip because I have a personal interest in them remaining open (if they go out of business perhaps I have to walk further for coffee). Ice cream shop, I unfortunately just care less if they go out of business.