I don't understand what "crawled up your ass and set up shop there" mean here. What's it mean?

Native speaker’s answer
Rebecca
This is considered a vulgar sentence. It implies that something is "up his ass," which means that he's rude and easily offended or uptight. This is considered an offensive statement, so just be careful where and to who you say it! Ex: What? have you got a stick up your ass or something? Ex: The woman acted like she had a stick up her ass the way she treated us.