Boot is indeed a British term for car trunk. It's what my parents always said it was called when I was a kid, and it's what I'll probably say it is to my kids, if I ever have any.
You can still say I need to use the bathroom and everyone will know what you're talking about. Wee is just a word for urine that parents teach their kids to say because "I need to urinate" is a little advanced for a 4 year old. It's much like how Americans teach their kids the word pee, which we also do here.
Bathrooms are just rooms with baths or showers.
i've never heard of this term and i'm around british people around half of my day every day
i guess they're just really considerate of how american i am
Most likely. That or you just don't talk about the backend of cars very often.
