If I order a pizza for pickup and don't pick it up can they take me to court? Or legally pursue me?

Technically, they do have a legal claim against you, since your placement of the order and their acceptance of it creates a contract for the pizza. If you failed to pick it up and pay for it, this is a breach of the contract (unless there was some supervening event outside of your control that made it practically impossible to pick up the pizza). I wouldn't be too worried, though ,,, in our legal system, even a victorious plaintiff must pay its own legal fees and court costs, and it's hard to imagine the shop owner spending hundreds or thousands of dollars to chase down a $15 order, unless this happens a lot to them and they want to make an example out of somebody. Of course, they could appear in court on their own behalf without counsel, but this still seems like a waste of time. So, this strikes me as a scare tactic more than anything else.