> Other than this my friends are pretty good people

I have a hard time believing this if they use the tiniest reasons to not tip very hard-working service staff. I mean, this alone makes them by definition bad people, full stop.

Advice? Tell them you will no longer go out with them. That's what I'd do, I would not be able to be associated with that, it's so insanely disrespectful of someone that relies on you, especially larger parties, to pay their damn rent. And you're a damn saint for covering the difference, you should stop though, this isn't your responsibility.

Almost all problems servers have are not their fault, they are usually just the "messenger":

• they aren't responsible for bad food
• they aren't responsible for food that is late
• they aren't responsible for bad management

I find it's quite rare that i can attribute a problem in a restaurant to a server