IMHO depends on the amount. If you are severely dehydrated and you notice your stool physically hurt coming out. A small amount of blood might honestly not be unexpected.

Edit: To be clear “severely dehydrated” is kinda an important factor here. Point being that if the cause is obvious I dont see why you’d get a colonoscopy. Please correct me if im wrong instead of just downvoting for anyone who knows more about this thx ^^

It doesn’t matter. Go. See. A. Doctor.

Why is the amount that you care for your own ass so ant-sized?

If you are consistently severely dehydrated that’s also a good reason to see the doctor ;)

But yeah, if it happens once it’s not necessarily a problem. It’s when you keep having bloody stool that it’s a good idea to get checked.