Rachel's boss, Kim, (guest star Joanna Gleason) is said to be annoyed and passive-aggressive with Rachel. She even attempts to avoid her at first. However, in the prior season ["The One Where Rachel Smokes"], the two are on good terms. They have lunch together and smoke multiple times. There is no explanation given for this sudden change in attitude/demeanor between seasons.
When Ross's date with Hillary goes south when the black light comes on, if you listen to his speech very carefully it sounds inhibited when he says, "what's the matter with me!? You've got a black light it's 1999!" It sounds like he has a slight lisp possibly due to wearing a retainer to make his teeth glow. This goes against what he says earlier when he says he used a gel to whiten his teeth. This is pure speculation though.
When Rachel enters the elevator at about 6:30, she says hi to Kim as she reaches to push a button, but doesn't actually push a button.