1. It’d be an interesting study to see how church attendance affects individual behaviors. In other words, is the evangelical a better tipper on Friday night than Sunday afternoon? Are group dynamics at play? Late vs. early service grumpiness? I suspect that the proselytizing and Chick tract stuff goes way up after church, but the money thing would be interesting to learn.
2. Setting aside the day of the week issue, the treatment of the Sabbath is addressed a few times in the New Testament, both by Jesus and in the Epistles. I don’t see any biblical justification for an outright prohibition on going out to eat after church, although individuals might make different choices based on their own conscience. Using the Sabbath as a gotcha betrays a preposterous reading of scripture that nearly matches the ones found in some evangelical churches. Using the Sabbath as a gotcha is also what they did to Jesus, so checkmate, atheists.
3. when I worked as a server, the jerks and cheapskates seemed to come pretty randomly. The stereotypes never seemed to hold up for me. I was also terrible at my job, so the difference between a bad tipper and a reasonable tipper wasn’t significant.