What is euphemism? Don't be too formal, just be correct.

Euphemism means not being positive, being more acceptable, not hurting the other person's face too much, but making people understand what you mean (if it is too euphemistic, it is impossible for everyone to understand).

It's like:

You invited me to go shopping this afternoon, but I didn't refuse and didn't want to go with you. Let me put it this way: I have something to do this afternoon, or I'll make an appointment with you another day. . . . . .