In what I hope was not a sign of declining mental faculties, I covered up my leftover pizza with foil, then promptly did not put it in the refrigerator. I’m still going to bring a couple of slices with me for lunch, but should I eat?
It’s pan, in case that matters, and yes, lots of cheese.
I have no training in the health sciences. As one data point, however, I have done something similar numerous times and lived. Leftover pizza is too valuable to waste.
You obviously weren’t a partier in your youth. Leftover counter pizza and beer makes the best morning after breakfast.
No, I was not. 
Does it matter if, between visiting for the holidays and stuff, I might not finish the leftovers until next Tuesday? It is now in the fridge, of course.
I assume no liability for my answer.
First, putting foil on pizza is not a good idea. The tomato sauce (if any) will react with the foil after a few days. It’s up to you, but I’ve run into this problem on several occasions.
Second, I doubt that 12-15 hours at room temperature will cause any harm. I’ve eaten a lot of pizza from boxes that were out on the table from the previous night. It’s (basically) bread, cheese, cured meats, veggies, olives, and other ingredients that are unlikely to spoil quickly. Now, if you get raw chicken on your pizza, that’s a different story.
Again, also not a scientist, but vast untold thousands upon thousands have eaten cold leftover pizza from the box on the counter the next day. Maybe we’re all ill with low-grade botulism, who knows, but I’ve never given it a second thought. (Although I do generally put it in the fridge, honestly I do.)
I’ve also eaten cold leftover pizza. And actually, in my mind, one of the things that separates good pizza from bad pizza is how it tastes the next day cold. A good pizza still tastes great that way. But a bad pizza (Pizza Hut pan pizza, for instance) tastes awful that way. And it’s not much better heated up.
I buy a pizza every Monday (on special). We have a few slices with dinner and I bring the remainder to work. I never refrigerate it. Never. Sometimes it is still being eaten on Wednesday.
In my experience, it depends on where you live. If you are in the South (see relevant thread), there is a good chance that creepy crawly things have visited your pizza in the middle of the night. If you are in a more wintry climate, there is less danger of bug exposure.
Presuming you’ve cleared that hurdle, my main concern would be the palatability of the cheese. I have absolutely no expertise in this, but I imagine bad cheese would not do well in your digestive tract.
Just stick the slice in a 350 oven for about ten minutes before consuming. That should be enough to kill any germs, bugs, or rodents that crawled into it overnight.
Unless the pizza is topped with potato or chicken salad it should be fine.
yeah - but then it won’t be cold pizza - and warmed up day old pizza is rarely that good (no matter the brand).
Ah, pizza the perfect leftover in any condition. Eat and be happy!
When the then-future Mrs. L.A.'s father died, I helped her cleaning stuff out of the house, giving her emotional support, and going to the family gathering with her. She’d ordered a pizza and intended to leave the leftovers on the counter overnight. When I said it should be put in the fridge, she said she always left the leftover pizza out. Sorry, but that just skeeves me out. Anyway, since she moved in with me seven years ago, I don’t think she’s left pizza out.
Ah yes, pizza and Chinese food: even when they’re cold, they’re still pretty good. Or is that pizza and sex?
Never mind. OP: Pizza will not spoil on the counter overnight. It is known.
The pizzeria I patronize gives me a pie that heats up next day almost as good as the fresh item. I won’t argue, but I could mail you a slice and you could experiment…
I’d add fried chicken to that list.
Actually, I daresay some pizzas are even better reheated (if you reheat them in a cast iron pan with a little bit of oil–these are the pizzas that aren’t crispy enough to begin with. I’ve had several pizzas that were so-so fresh but just spectacular reheated that way.)
You should definitely not eat that pizza and instead you should send it to me and I will dispose of it properly and thoroughly.
We have literally never put pizza in the refrigerator. Not even when I was a kid. Wrapped in foil and left on the counter.