“I also think it’s OK to give teachers a gentle way to dissuade students who ask them for a recommendation.”
My advice to all students, at all levels:
YOU WANT TO KNOW if the teacher/professor/boss is less than enthusiastic about you. The way you ask can invite candor, or deter it.
Don’t start by asking for a recommendation. If you ask, “Will you write for me?” the only options open to the teacher are (1) writing the letter and (2) refusing to write the letter, which is awkward and difficult. A lot of people will say “yes” for letters they don’t really want to write. You don’t want that lukewarm letter.
Instead, start by talking to the teacher/professor/boss about your plans. See what they have to say. Nine times out of ten, if you’ve picked the right recommender, they will say, “Do you need a recommendation?” But if they act like they don’t want to be there, or they try to change the subject, or they seem like they’re in a big hurry to get the conversation over with…well, that’s valuable information for you, and you can walk away without getting stuck with a mediocre letter.