A thousand calories of peanut butter is
one cup, 8oz, of peanut butter.
Maybe 4 or 5 good spoonfuls.
I'm willing to bet that almost any healthy adult could down 4 spoons of peanut butter w/o issue, and that most people would end up being way over their calorie limit for the day as their body wouldn't go "yup that was lunch and half of dinner! All good now!"