Eating old peanut butter will rarely make anyone sick especially if the peanut butter has been sealed up and is just expired.
Just because the peanut butter is expired it doesn't mean that it has to be thrown out.
When peanut butter expires on an expiration date it just means that the peanut butter is not as fresh as it was when first packaged.
I've eaten putter that I've kept sealed way past the expiration date and never gotten sick from it.