I made some "bad idea" beers early on. I may have inadvertently started the peanut butter and jelly trend... thankfully a dozen years later the Northern Brewer forum is gone, along with all of the evidence.
My take is currently that anything with preservatives, oil/fat, artificial flavors, and other complex ingredients does not belong in a beer. It might be fun to say you fermented it, but you can absolutely get better results using base ingredients without everything else mixed in, and it will cost a lot less. If you must, buy deyhdrated peanut butter powder and an artifical grape flavoring and add that... in no case should you add whole reeses peanut butter cups and purple skittles.