1. 'bottom' and 'behind'. Your bottom is the part of your body that you sit on. You can use bottom in conversation and in most kinds of writing. If she could change any part of her body, it would be her bottom. Speakers of American English usually say behind rather than 'bottom'.
Peanut Flour, unopened 1 year. Peanut Flour, opened 2-3 months Lasts up to 9 months in refrigerator. Peanut Oil, roasted, aromatic, unopened 9 months. Peanut Oil, roasted, aromatic, opened 2 months Lasts 4-6 months in refrigerator.
The answer probably depends on how long it takes you to consume the peanut butter once you have opened it. In our household we never refrigerate our peanut butter. (It is most often from Trader Joe's, with the only ingredient listed being dry roasted peanuts.) An open jar of peanut butter in our household typically gets consumed within 6 weeks' time, and we have never had any problems with the peanut butter going bad. Yes, if you don't refrigerate your peanut butter, it will go rancid more quickly than if you had refrigerated it. But it will likely take a number of weeks or possibly a couple of months before that occurs. I suspect that peanut butter made with raw peanuts rather than roasted ones spoils more quickly.