Alistair: Well, I would be content if my Mimi would just lay off the cheeseburgers
This wouldn't have been the first time that a Mimi didn't look the part of a woman dying of consumption. Legend has it that the soprano who performed the part at the premiere of La Boheme in 1896 had wasted away to 300 pounds.
Up until this point, although Gil Chesterton is portrayed as gay in manner and speech, there has been no admission on his part that he is, nor has the show offered any such evidence. During the end credits, we finally see Gil actually doing something that indicates that he is in fact gay - namely, going into a gay bar (Bad Billy's).
Roz: (in disbelief at Frasier and Niles' fawning obsequious behavior towards Alistair Burke) Wow, that was thorough. Find any polyps up there?
Roz: Do you know what Barry was doing from ten o'clock until midnight last night?
Roz: Me, that's what!
Martin: Let's see. One of my sons just got picked up by a guy. My other son is jealous. Yup, life is good.
Frasier: He does not think I'm gay!
Niles: He thinks I'm gay, and I'm standing next to my pregnant wife!
Alistair Burke: (To Frasier) Sorry, my angel!
Niles: Well, it looks like Nigel won't be the only one giving up his seat tonight.
Title: The Doctor Is Out
This is likely meant as a (gay outing) variation on "THE DOCTOR IS IN", the sign displayed by Lucy (a psychiatrist) in the Peanuts comic strip.
The scene six title is "THE QUEERNESS OF YOU". This alludes to the song "The Nearness of You", written by Hoagy Carmichael and made popular again by Norah Jones.