Bottom line, I feel like the culturally accepted baseline tip percentage must be raised from 15% to 20%. If you want to tip less than 20%, that's takeout territory, but if a human is actively waiting on you and serving you, 20% should be the minimum percentage.
Hell, I barely ever go out. Often can't afford to. But when I can, it's always 20% as a starting point and I often round up if it's not a round dollar. Restaurant work sucks and sometimes workers can have bad days and slip up here and there, but even if my server is having a tough time, I tip at least 20% because I know they likely need it more than I do.
To the monsters who decide to tip nothing when waited on, even if it's takeout or counter service, or the douchebags who leave $5 on a $50 tab because “It's not my responsibility to pay your missing wages” I want you to know that you're the asshole whose friends don't like going out with because it makes them feel awkward that you don't tip, AND your friends likely overcompensate for your shitty tips too.
Everyone… If you discover a friend of yours is a shitty tipper, call them out on it.