Saying yes feels good. Saying no can also feel good when it is the right no, delivered properly. Why is it sometimes so hard to say what we mean? Of course that is assuming that we even know what we mean or what our preferences are. If not, then it is time to ask yourself, without filters of job, your friends and family, your schooling and any other expectation that has been placed at your feet.
In the end, it benefits everyone to just be direct. A simple, kind and gentle, no or yes. No excuses. No elaborate explanation needed. You have a right to agree or to decline. Everyone does.