Is it bad to eat a peanut butter sandwhich before sleeping?

It is not bad: Hunger can worsen sleep. A light snack before going to bed (not a heavy meal) may help sleep. As long as you avoid stimulants caffeine, tobacco), it does not really matter what you eat before going to bed as long as it a light snack, not a heavy meal.

Likely not: If a peanut butter sandwich is part of an otherwise balanced diet, having one before sleeping would not matter. You should brush your teeth after eating and before going to sleep.