I think that it is far worse when you warily sing your new song for the first time and the listener tries to convince you that you have written an existing song.

This can be done in subtle (and sometimes innocent) ways, like saying. "have you heard _______ ____'s song called _________"?

Or. "that, reminds me of ________"

The time for saying these things, for the right reasons, is probably not when the writer is feeling the way Bert describes above but a little later when they a bit more confident.

If you are saying them for the wrong reasons, of course, it is exactly the right time.