How do you get a kid to eat something other than peanut butter?

Try getting him to take 4 bites of something else first, then give him the peanutbutter. Tell him fine, he can have his peanutbutter, but he must give you what you want too, and that is 4 bites of meat, veggie, cheese, whatever. He may discover he likes something else, despite himself.

LOL, well it IS a good source of protein. :) More than likely it is just a phase he will give up when he's ready. Until then, encourage him to eat some of the other things by adding something with peanut butter to your meals (even if it's just for him). Peanut butter is good on celery & would provide some necessary roughage. They even have peanut butter ice cream. Peanut butter crepes, on toast, with carrots as dipping sticks, peanut butter brownies or muffins or cakes, etc. Phases can be long or short term & unfortunately vary by the person. Hopefully he'll outgrow his sooner rather than later. :)

Maybe try to put peanut better on other foods. Peanut butter and banana, peanut butter and celery with raisins? You may wanna try other variations, it may look bad tasting to you, but your son may like it.