Fridge Logic: You can buy condoms in America. I wouldn't be surprised if they're also cheaper than in Britain, but I don't feel like searching for comparative condom prices on the internet. Rule of Funny definitively applies though.
It's a CMoF, because Colin is so convinced that he'll find girls who love his accent in a heartbeat, which might not give him time to find a place to buy them... which as it turns out, he's entirely correct about.
Fridge Brilliance: Joanna does fancy Sam and her pointing at him first during "All I Want For Christmas" was her way of saying it to him, without actually say it (she is a preteen girl afterall).
And then she points to everyone else, singing "And you, and you," making Sam think it was all part of the song and kicking off the airport scene.
Harry really does still love Karen - he buys Mia the first pretty bauble he can find, but gets Karen a gift that he knew she would like because he listens to her, and knew she would appreciate because he knows and loves her enough.
Fridge Horror: Not really horror but more sadness. Mia says Mark isn't her boyfriend and we see him being friendly to her. He's trying to get over Juliet and the girl he's trying it on with is pretty much rejecting him in favour of a much older guy.
Or not. In a deleted scene Mark and Mia sit in the art gallery and she tells him she's planning an affair with Harry. When Mark says it's probably a bad idea since he's married, Mia casually suggests that maybe she and Mark should start an affair instead. Mark laughs and when she asks "why not" he answers that they should just leave it at that.
It may be a Crowning Moment of Funny, but the scene where the Prime Minister tells a person "Sorry things have been so bad. It's my cabinet, they're absolute crap. We'll try to do better next year" has serious implications. Just how bad do things have to be before the Prime Minister admits how useless the cabinet is?
This might be more of the signature British self-deprecating humor though. Has there been any British prime minister and cabinet, especially in the more recent, cynical times, which was not called crap during their term?
It's self-deprecating humour. It shows the Prime Minister is in tune with what the electorate is thinking (which is almost universally that politicians are incompetent) - which was a big complaint about Tony Blair at the time this film is parodying him. It's why we also see him doing things like being puzzled by the attitude towards Natalie's weight and eventually standing up to the US President. It's a sort of "genre savvy" character, if the "genre" was "what the public really wants" (as opposed to "what would be realistic for a real prime minister to do").