Bad Manners and Brimstone

To be fair, there are parts of the world where - in some classes of society at least -  not only is picking one's teeth at table perfectly acceptable, for men using one's own personal bladed weapon for the purpose is considered dashingly macho. But I've never heard of any culture in which licking the plate is a done thing.

Rural communities used to have barn-raisings, right?  And quilting bees, etc.  Those were hard work.

I guess it depends if it's a community custom, so everyone takes there turns helping and being helped, with jobs that are hard to do all by yourself.

So I think I'd feel better about this in a context like that, or otherwise just a very small group of close friends and family doing one or two relatively pleasant projects, like maybe painting one room or assembling nursery furniture and toys.

I once had an experience where the meal took an incredibly long time, but not for want of wait staff. We could see waitresses running around, getting salads out and making sure everyone had drinks and refills. But the food being placed on the pass (we could see it from our table) was intermittent, if even that. Finally, when our waitress came by to check our drinks and reassure us that our food should be out shortly, I asked if there was a problem in the kitchen. She paused and then said, "Only one cook showed up tonight." Fortunately, all salads were prepped and so the waitresses were able to handle that. But this was on a Friday night, and the restaurant had advertised an All You Can Eat Fish special.

Those poor waitresses! I left a huge tip because they were trying so hard to make it work. (We also witnessed two waitresses arguing in hissing tones over whose spaghetti dinner that was sitting on the pass, the one with the older order claimed it).

On the other hand, we have never gone back to that restaurant. They may still be open, at least there is still a sign on the building.

My honest opinion is Sally is a jackass. She should have realized this server was running her ass off, and doing the best she could. All it takes is a brief look around. Then, she is going to call you "stupid" for how you choose to tip? And she wouldn't have left a tip at all, sorry she is a really bad word that I'm sure I can't say here.

The manager definitely should have been helping her, unless they were in the back helping a short staffed kitchen.

What you chose to tip is none of Sally's business and her commentary wasn't needed. Let alone an ad hominem attack.