My favorite delivery is to "drunken relatives". Basically, it happens like this: You have a bunch of drunks who try to out-tip each other at the door. If they're drunk enough, they bid against each other, and if you're lucky, they BOTH end up tipping you. Sometimes in excess of the value of the orders.
My worst is pizza delivery to churches. I've never received a tip from a church or church organization, and they usually want you to act like a caterer and set up and manage the pizza table. If you're lucky, they have the money ready, and you don't have to wait for 30 minutes for the person with the money to show up. All the while you are losing income waiting for them...
Overall, it's a nice job if you are big on being independent.