The "dumped dates" comment is a reference to the time he had lunch with Maureen Dowd 10 years ago. It wasn't a date, just an interview type thing. Dowd's comments about that decade-old event in the Newsweek cover story hit piece on Rush sounded like things a "dumped date" would say.
It's a subtle shot at Dowd, but one that's richly deserved. Of course I guess just about every shot at Dowd is deserved.
I believe that there was an actual reference to women had dinner with him and who found him uninteresting.