I'm getting a carry out order from a sit down restaurant, but I'm not going to tip when I pick it up.
Why wouldn't you tip? Isn't the restaurant still serving you?
They were very slow to take my order and even slower to bring me my food.
It is appropriate to tip when you are receiving service from a restaurant. If you do not like the service, then you need to speak to a manager so that they have the opportunity to improve their service.
I don't have to tip when I'm not satisfied. If the service sucks, I feel no need to tip.
The server who prepares, packs, and brings your food out might not be the one who's responsible for the wait, though. What if the chefs were being slow? You'd be taking the tip money from the server for something that they couldn't control.