Some people, when criticised, will tell you ``Don't be judgemental!'' in fact, being judgmental means putting a value judgment onto something, whether good or bad. It seems relatively rare for somebody to say that if you say something good about them, but that is still being judgmental.
I get the impression that what they really mean is ``Don't criticise me! I'm prepared to use emotional blackmail to stop you criticising me!'' of course, the irony escapes them that they are judging that you are being judgmental.
One example of somebody being fair this way is Jesus saying ``Why do you call me good?''