But you don’t want to sound like you’re not a team player. And if you say “that’s not my job” to a supervisor or colleague, you’ll sound like a poor sport, as well as severely jeopardize your future and reputation.
Propose this as a solution, or suggest that you do part of the assignment and another team member (maybe even the person asking) does another portion — again, reminding them of everything else you have on your plate.
Of course, there might be occasions when you simply can’t do the work the other person is asking of you. If you can’t do it, say so. Avoid being rude (for example, those four risky words: “That’s not my job”).
Explain what’s preventing you from completing the task, and, if you can, suggest alternatives, such as additional resources. Being seen as a problem solver, rather than disrespectful, rude or uncompromising will be to your benefit.