In # 3 of Season 6, Dorothy is tying Stanley's bow tie and says she remembers the last time she did that: the night of their senior prom. However, in # 22 of Season 6, the entire storyline is about Dorothy being reunited with John Naretti: the guy who stood her up for her senior prom.
Toward the end of the episode, Dorothy sits on Sophia's lap. When she stands up, a boom mic is visible in the upper left.