Can you get food poisoning from pizza left out on the counter (in the box) overnight? what about a couple days?

Food Poisoning: Definitely are more at risk as food borne bacteria have the chance to proliferate at a higher rate at room temperature.

Yes: Food poisoning can be caused by viruses or bacteria. They can reside on foods and the longer foods are left out to spoil, the higher likelihood this can occur. Symptoms can include nausea, vomiting, abd pain, diarrhea, or fever. Symptoms can start as early as several hours after ingestion. Best to rest and hydrate, while eating smaller meals with less fat content.

Possible: Depends on degree of contamination and the germ, or germs! best trashed!