To me just generally the way Tom is always so polite to Hal. Even when he and Alex have Hal strapped to a chair and he's screaming obscenities at them, calling them a "hound" and a "bitch". It's just something about his voice when he goes "Don't be rude, Hal".
Tom's response to Hal asking him why he has the materials for bomb-making in the house and cafe.
Tom: Mcnair told me to be polite and kind and always have the means to make to a bomb.
"If you see a big scary man with a burn on his arm, run!"
Tom and Hal's attempts to chat up Michaela.
Tom: "I like your tights, you look like a bee and I like bees."
Tom finding out George has not given the baby a name yet.
"Even McNair gave me a name, and he ate me parents."
The "Alex's Kicked the Bucket List" minisodes are adorable and hilarious. Her ghostly goals include kissing Robert Downey, Jr (Hal: "You are not kissing anyone without their permission!"), getting revenge on Rook (a plan which would have involved Tom stealing a cow, had it not been for Hal's intervention) and getting wooed in Paris (the closest they get to that is Tom taking her on a dinner date while Hal serves as their waiter, while dressed as a stereotypical Frenchman. He is not amused).
Alex justifying why she let the new vampire Crumb go from the cellar, who Hal had tied up there.
Alex: How was I supposed to know he was dangerous?
Hal: You're right, I should have left you a clue, like tying him to a fucking radiator.
Tom mocking Hal's accent to provoke him in the Employee of the Month competition, then spinning his cleaning spray like a gunslinger while Ennio Morricone's western compositions play.
Tom: You know when I transform, I should drag you around on a piece of string in the woods. (Pause) I'm saying you're a chicken."
Hal: Yes, thank you I got the analogy.
Alex's exasperation over having to look after the ghost of a bratty Victorian child, especially when he gets Tom to fuss over him, even though the kid is obviously faking.
Alex: He's been dead for two hundred years! I don't think he can get much more poorly than that!
There's also her reminiscing about how her little brother would use the internet to look up illnesses he could pretend to have, so he could skip school. Because he tended to not bother looking up what the sicknesses actually were, he once tried to convince Alex he was going through menopause.
Alex's attempts to discipline Oliver:
Alex: (attempting to drag a struggling Oliver to the "naughty step") He's a freak! He can't play football, he thinks television is vulgar, and don't even get me started on the racism!"
Alex finally getting to play the piano, where she brightly declares that she's not lost her touch at all, despite being painfully out of tune. The looks on Hal and Tom's face says it all.
Then, there's the aftermath. The manager fires Tom, but wants to keep Hal because she's smitten with him. Hal angrily gives a moving speech in Tom's defense, saying that Tom is a fine employee, that she shouldn't pass over a hard worker in favor of someone attractive, and that if Tom's fired, Hal's quitting as well. Cue the next scene of them both leaving the hotel.
Tom: Well that was stupid. Now neither of us have jobs.
Hal: I was looking for "Thank you".
Captain Hatch's reaction to two werewolves walking into the room.
Hatch: It's like Battersea Dogs' Home in here.
Crumb dressing up like Hal as part of his rehabilitation.