Chips = crisps, e.g. "I'll have a bag of crisps."
Fries = chips, e.g. "Fish and chips are mankind's greatest culinary invention."
Cookie = biscuit, e.g. "Want some tea and biscuits?"
Oatmeal = porridge, e.g. "Porridge for breakfast on a cold morning is divine."
Raisins = sultanas, e.g. "I'm putting sultanas in my porridge."
Eggplant = aubergine, pronounced "OH-ber-zheen." Sort of. Ish. It's hard to write phonetically.
Pants = trousers, e.g. "My trousers are too tight."
Underwear = pants, e.g. "That girl's dress makes it clear she isn't wearing pants."
Sweater = jumper, e.g. "You don't need a coat, just a warm jumper."
Sneakers or tennis shoes = trainers, e.g. "It's raining and my trainers are soaked."
Nylons = tights, e.g. "I snagged my tights. Do you have nail polish?"
Tights = tights. O….kay.
Cents = pence (or "pee"), e.g. "That'll be 50 pee." Now imagine if 50 Cent were from the UK.
ATM = cash point, e.g. "I got mugged at that cash point."
Store = shop, e.g. "I'm going round the shops to buy some trousers."
Drugstore = pharmacy, e.g. "I have a wicked hangover. Where's the pharmacy?" DO NOT say drugstore. People will assume you are looking for something quite different, and may direct you to Brixton.
Band-Aids = plasters, e.g. "I cut myself! Give me a plaster."
Vacation = holiday (or "hols" for short), e.g. "Suzie's on holiday."
On the weekend = at the weekend, e.g. "I'm going to Brighton at the weekend."
To rent = to let
Bathroom/restroom = toilet (or "loo"), e.g. "I need to use the toilet." (Otherwise, prepare yourself for the inevitable, "What, are you going to take a bath/have a rest? Haw!")
Monkey = You know what? Don't call anybody this. It's not considered cute here.
Exit = Way out, e.g. "The building's on fire. Where's the way out?"
Elevator = Lift, e.g. "Take the lift to the fifth floor for haberdashery."
Sidewalk = pavement, e.g. "That fucking bike just drove up on the pavement!"
Gas = petrol, e.g. "I have to stop by the petrol station."
Truck = lorry, e.g. "Mind that lorry." "What lorry?" splat
Drunk = pissed, e.g. "No, I am not sitting on the pavement because I'm pissed. It's comfortable."
Cigarette = fag, e.g. "Got a fag, mate?"
Spliff = spliff (Hooray.)
Asian = Indian, Pakistani (Use "East Asian" for other flavors, e.g. Japanese, Korean.)
Ass = arse, e.g. "What an arsehole." Although I find this one sounds funny in an American accent.
Lots = loads, e.g. "There's loads of these little idiosyncrasies that one LJ post won't cover, but these are the important ones if you don't want to be mocked or seriously misinterpreted."
AND LAST BUT NOT LEAST
Soccer = football.