"Greg and Darma" Greg? They always call him "Hotch", but I forget what his first name is on the show.
Oh, and you know the guy who was in Buffy? He plays a nerd here (well, he played the nerd Xander on Buffy, too!

) Anyway, he and Penelope apparently were at her place (mmm hmmmm!) when Rossi showed up. Nerd was upset (interruptus), so at the end of the episode, he asked Rossi, in front of everyone, if they could have a man-to-man chat. OMG! JJ started singing, "X and Penelope, sittin' in a tree..." Reed, of course, had never heard the song before and didn't catch its significance, and Paige didn't want to explain.