Great thread. I love regional differences, they are really interesting.
I have a hard time identifying things from my own upbringing in terms of region because my parents are from two different parts of the country (California and Oklahoma), met and married in Germany, and we lived all over the country (military). I get the oddest looks from people sometimes because I regularly use slang terms from all over the place, and they can't figure out where I'm "from".
My best friend loves to get me to say "dog" and then she tries to say it the way I do. I often pronounce it the way my grandmother does (born in Alabama, moved to Oklahoma as a teenager) which sounds like dowg (ow in the middle, as in ow that hurt). My friend can't say it. Makes her laugh. I can say dahg the way people say it here, but it only comes out that way about half the time.
It is not particularly unusual in the PNW to order tartar sauce with your fries, whether you are having fish or not. Doesn't get you any weird looks. Beyond WA and OR, I've gotten the strangest looks for asking for it.
Went to Canada and was completely taken by surprise to be offered gravy with my fries. HUH?
In WA if you order "tea" you get hot tea. If you want iced tea you have to say so. Most places do not serve iced tea pre-sweetened...which IMHO is a crime against nature.

Sugar simply does not properly dissolve into cold tea. When my relatives or friends visit from other areas and order "tea" I jump in to translate and warn them that it won't be sweetened. They usually change their order.
Of course I learned the hard way in VA that when I wanted hot tea I had to say so. Just saying "CUP" of tea (as opposed to glass) didn't cut it. I drank a lot of iced tea that I didn't really want first thing in the morning until I fixed my lingo.
I have an English friend that I've known for 8 1/2 years via private message board, who was grossed out for over a year by me talking about making biscuits and gravy for my husband before she finally said something to me about it. Of course a biscuit to her is a cookie, and she had no idea what we call a biscuit. Another English friend of both of ours, who now lives in Canada, explained to her that our biscuits are "rather like a savory scone, except of course scones are nicer."
Same English friend made me laugh by talking about her daughter wearing her husband's jumper. What she calls a jumper I call a sweater. What I call a jumper, she would probably call a pinafore. I had the most hysterical mental image of her husband prancing around in a dress. He thought it was pretty funny too, when she told him about it.
Fireflies (lightening bugs) - I grew up catching them, but now live in an area with none.
Various liquor laws when traveling - Some places have dry counties, other sell in grocery stores.
I walked into a bar area in Washington state with my DD (age 5) to swipe some napkins off the bar because she had a cut that was bleeding and the bartender freaked out that she couldn't be in the bar area (we were waiting for our table at the adjoining restaurant section). In my area, having kids in bars in no problem legal wise. Many local bar and grills are pretty packed with families early in the evenings.
We do have kind of an odd law about that here. The way it works is that children can be in bars that serve food only during certain hours (I think they have to be out by 9 pm), only in the dining area, and ONLY if there are at least two steps (stairs) separating the dining area from the bar area. Which always struck me as kinda funny. As if the kids couldn't possibly climb the stairs? And you can bring all the alcohol you want down the stairs anyhow so...why the stairs?
