Just watch it for a bit. If it doesn't make any attempt to move, eat it.

I don't think that a pizza has ever survived long enough for this to come up for me, but Friday to Monday in the fridge would be fine, I'd have said.

what is this 'leftover' pizza you speak of?

That's fine. The main loss at this point is texture/dryness. I like to fry old pizza in olive oil in a skillet, then lid with the heat off for a minute. The steam melts the cheese and it comes back to life.

My standard for anything is that if it's not moldy, it's fine.

Until breakfast the next day when it's eaten cold.

As long as it doesn't have sea food or chicken I'd expect it to be fine for a week in the fridge. Ideally, you put some kind of cover on it to protect it from spores.

Normally 7 days is the maximum

Depends on the topping, fish no, margarita yes. Chicken - check your access to a toilet for the day.

Op is not obese.

Sorry, I don't understand the question.

I guess it also depends on the toppings. Like, seafood and big chunks of vegetables spoil faster than, say, cinnamon sticks (but the latter is quite a rare sight on pizza). At least if you care more about the food safety aspect.

Otherwise, if you were just looking for various opinions (or preferably, equivocal ones), I personally wouldn't eat it later than the second breakfast time. I mean, the breakfast two days from delivery, not the hobbit meal. Also, if it's as late as the 2nd day, I wouldn't do that on a work day, or if I'm not guaranteed to have a safe emergency toilet opportunity.

If it's not slimy or furry I'd probably nuke it in the microwave and still eat it up to a week later.

A few days is fine.