getting someone sacked for having a bad day is a scummy thing to do
It is, but only because losing a job means that person might now lose access to food, housing, and healthcare. That's a really steep price to pay for what could be an isolated incident. But that's not something to lay at the feet of the person tipping here. They are also a victim of the structure we've created. They need to choose between shutting up and accepting verbal abuse in their own home or speaking out and possibly triggering events that ruin the delivery driver's life? Neither of those choices are acceptable.