My mom waited tables for ten years and my dad worked as a line cook for several years as well so I just don't fuck with restaurant staff or service staff in general on general principle.
I don't fear the retaliation from the staff, I just don't like to make someone feel like shit unless they truly deserve it, and the person filling up my tea glass at Applebee's ain't on my shit list.
Also I work in a service job and I really don't want to be the one asshole who ruins someone's day.