let me re-phrase my clumsy statement. What the critic said i.e. "nice song, shame about the bum notes" may have been true. telling you this is impolite.
I don't make a habit of criticising performers but I will tell someone if their instrument is way out of tune. As I have said before the setting is an important factor. If it is a public setting I would not be surprised to receive comments about a performance.
john