Well the US is completely different from our friends in the UK. Like to greet my friends I would say "What's up dude?" or "What are you getting into today?"

So in the US, many people have a preferred soda (MTN Dew, Coke, Pepsi etc). So if you offer a soda they don't really like it is perfectly acceptable in the US to just say no thank you. We would see every soda and other drink options as a choice Example: Coke, Pepsi, 7-Up, water, milk and juice would be 6 choices. Maybe it's because the US drinks more soda (and junk) than the other English speaking countries. Die-Hard Devotion (in this case) is a phrase that means that you ONLY drink a certain type of soda and no other.

People shouldn't be shocked. In the US this is a perfectly acceptable greeting. If I was greeting someone formally in the US I would say "How are you?" and my friends I would say "What's up?"

Child care center. Never heard it said this way in the US so it must be a UK phrase.

It's a mild insult that we use mostly when we are joking. When you call someone a shrimp, you are saying they are small and cannot defend themselves basically. If someone in the US (my home) called me a shrimp and was completely serious I would begin laughing.

The phrase basically means "once in a long while"

We do this sometimes in literature. Good writers avoid repetition in order the make the story more interesting.

It doesn't make sense unless Flow is the name of someone they are talking to.