[wccrawford]

"if someone had shouted this in a supermarket or bank line, what would happen?"

They've have been thrown out of the store for sure. They might also have been banned from the store, depending on how it escalated and how they reacted to being thrown out.

The police would have been called if they were banned, and maybe even if they were just thrown out for the day.

Twitter has basically done the same, without the cops. And they even said how to get un-banned, which was to remove the comments that violate their TOS.