Being asked to do not your job actually happens quite often, especially to juniors. Juniors are not specialized yet and many people sees them as being able to be molded into whatever they need at the moment. Usually such requests are benign, that is the person asking doesn't realize there are other people better suited to do the job. Sometimes it's because the asker thinks that you're free or your current task is less valuable - such cases are more difficult to clear up. IMHO the proper way is to simply state that:

I think that team X is better equipped to do this job. / I believe this is within competences of team X. / I don't want to step into team X competences. / Please clear that with team X, I can't do their job behind their backs.

If that fails, or you don't know who's job is this: This task is outside my competences. Or simply: I shouldn't be doing that.

You have to put emphasis on being unfamiliar with company procedures for this task (therefore likely you're going to do it wrong) and/or not infringing someone's else turf rather than "I just don't feel like doing it." The important distinction here is that we're talking about the job you were hired, company trained and paid to do, not a task you CAN do. Although, as a junior, you may get asked to do chores - that's unprofessional but comes with your low position in the pecking order.

Another angle is to apply the feudal approach: manager of your manager is NOT your manager: Please run this through X. If the executive insists, then state firmly I am sorry, but X is counting on me doing the task Y, I can't abandon the work I've been assigned to.

It's important to never back off: Once you state that someone's decision carries more weight than exec's whim, you have to run this to the very end, that is actually checking that with that person/team. Otherwise you're effectively admitting that it was merely an excuse.

Being asked to do not your job actually happens quite often, especially to juniors. Juniors are not specialized yet and many people sees them as being able to be molded into whatever they need at the moment. Usually such requests are benign, that is the person asking doesn't realize there are other people better suited to do the job. Sometimes it's because the asker thinks that you're free or your current task is less valuable - such cases are more difficult to clear up. IMHO the proper way is to simply state that:

I think that team X is better equipped to do this job. / I believe this is within competences of team X. / I don't want to step into team X competences. / Please clear that with team X, I can't do their job behind their backs.

If that fails, or you don't know who's job is this: This task is outside my competences. Or simply: I shouldn't be doing that.

You have to put emphasis on being unfamiliar with company procedures for this task (therefore likely you're going to do it wrong) and/or not infringing someone's else turf rather than "I just don't feel like doing it." The important distinction here is that we're talking about the job you were hired, company trained and paid to do, not a task you CAN do. Although, as a junior, you may get asked to do chores - that's unprofessional but comes with your low position in the pecking order.

Another angle is to apply the feudal approach: manager of your manager is NOT your manager: Please run this through X. If the executive insists, then state firmly I am sorry, but X is counting on me doing the task Y, I can't abandon the work I've been assigned to.

It's important to never back off: Once you state that hierarchy carries more weight than exec's whim, you have to run this to the very end, that is actually checking that with that person/team. Otherwise you're effectively admitting that it was merely an excuse. Once you get cleared with the new task, do your best.