What does 还真别说 mean? Some commented about a joke,


  还真别说，这个笑话有点意思。


The translator gives


  Don't mention it


I don't think it's right.
说 is the key to understanding. Here it means to judge, deny, or disapprove (especially quickly). 还真别说 translated character by character is "just really don't judge too soon". As a whole it means "(contrary to what I expected,) I just realize that...", or "admittedly".