If you call someone a stick-in-the-mud, you mean they are old-fashioned or boring and do not like doing new things or having fun. I felt sorry for him because he obviously wanted to enjoy himself but was married to a real stick-in-the-mud. Call me a stick-in-the-mud, but I just prefer the more traditional ways of doing things. Note: You can use stick-in-the-mud before a noun. He's going to let an opportunity pass him by, with his stick-in-the-mud attitude. Note: This expression is used to show disapproval.