For the Dutch:

  • Tapping the side of the forehead in the UK means you are stupid, not smart.  But many in the UK love the Dutch, so you will get away with it.
  • Also, you will give yourself away by inanely giggling at the fire extinguishers on the London Underground that say LUL on them.
  • The Dutch accent and word choices can amuse the British. Make the most of it and get preferential treatment!

Most American/Canadian/Australian/New Zealand travellers will be aware of certain words having different meanings, but just in case: -

  • Do not talk about fanny packs here! It will cause sniggering and some personal embarrassment on your behalf. Here, they are "bum bags". (The reason is that in UK English, a 'fanny' refers to the female reproductive parts). A "bum" is a bottom, posterior or rump, not a tramp or homeless person.
  • "Fag" is a slang word for cigarette, and not a derogative term to a homosexual male. The equivalent usage to the American word fag in this context are the terms word 'poof', queer and bent' 
  • Asking for the bathroom will generally be understood due to American programmes being broadcast in the UK. Toilets are usually referred to by a number of terms - loo is the most common but women may often say that they are going to the ladies or to powder their nose. Signs for toilets will often say this or WCs or on the street as public conveniences.     
  • Suspenders for trousers may be referred to as "braces", although these are falling out of fashion...
  • "Braces" are also metal wire contraptions used in orthodontics;
  • To 'wash up' means 'to do the dishes'
  • Jaguar is pronounced jag-yu-ar not jag-war;
  • Herbs not "erbs"
  • To most, "pants" in UK means what "panties" does in the USA.  Trousers is an adequately fine description.
  • "Flip flops" are what you call rubber footwear with a strap between the toes - not "jandals" or "thongs" (thongs over here are scanty "pants" known elsewhere as a g-string).
  • A "vest" is a sleeveless undershirt or singlet, not a warm sleeveless pullover.
  • Do not use the word 'ignorant' to describe someone as uninformed on a subject. Here, it implies intentional ignorance and is an insult.
  • Need a washcloth/face cloth? Ask for a flannel.
  • Aluminium = al-you- min-ee-um and NOT al-oo-min-um 
  • Tomato = to-mah-toe NOT toe-may-doh
  • Lieutenant is pronounced leff-tenant (though loo-tenant is slowly gaining ground amongst the youth).
  • To 'get pissed' is to be heavily under the influence of alcohol and not to be annoyed (which is expressed as 'pissed off').
  • 'Taking the p*ss' describes someone poking fun at another person.
  • Asking for Durex could lead to misunderstanding and embarrassment. It's not a brand of sellotape but a brand of male contraceptive. But a rubber is used to correct pencil mistakes.
  • Asking for the subway certainly in England will get you directed to a sandwich shop or an underpass.
  • Cellphone will generally draw a blank so instead use the term mobile.
  • The same applies to asking for an ATM. If you need one then ask for a 'cashpoint' or a cash machine. You may hear them referred to in a conversation as the 'hole in the wall' which dates back to the early days of cash machines when it is literally what they were. 
  • Gas is something you cook with and is not put into a car. Instead use the word petrol.
  • When ordering food, it's better to say "Could I have" instead of "Could I get", although people will understand you.
  • When ordering beer don't just ask for "a beer". There are three main types - lager (light beer), bitter or ale and many varieties of each.  If the choice is too much, ask the bar staff what they recommend.

Place name pronunciation guide (let's face it, British love to complicate matters): 

Leicester = Lester, Warwickshire= Warickshuh (similarly, Warwick = Warick), Gloucestershire = Glosstershuh (similarly Gloucester = Glosster) Bicester = Bistuh, Loughborough= Luff-bruh, Beaulieu = Byoolee (and not the Francophonic pronunciation, boh-lee-yuh), Edinburgh - Edin-bruh (not Edin-burrow or any other dipthongic concoction).

Witches and Itches - there's no logic here.  The following are pronounced with a w (ending in witch): Droitwich, Ipswich, Nantwich, Sandwich. The following are pronounced with no w (ending in itch): Dulwich, Harwich, Norwich, West Bromwich

The British also 'swallow' the '-ha' of place names ending '-ham' eg Durham, Nottingham, Birmingham, Cheltenham, Tottenham are sounded, Dur'um, Notting'um, Birming'um, Chelt'num, Tott'num, respectively.

It should be noted that while, in England, the "shire" in the names of counties is pronounced shuh, in Scotland and Wales, it usually rhymes with fire. Also, not all county names end with -shire, Devon is Devon and not Devonshire, unless you happen to be discussing the Duke of Devonshire, which is quite unlikely. It's like calling Florida Floridastate or Texas Texasstate. It sounds silly and is wrong!

Most Brits have problems pronouncing Welsh place names so most non Brits will struggle. LL is pronounced as cl with the tongue touching the top of the mouth and dd is an 'f''or 'th' and this is just for starters.  Some of it is knowing how to break the name down into pronouncable parts. Aberystwyth = Aber-ist-with. 

In Conclusion:

The above is, of course, an exercise in semantic pedantry (as well as sounding remarkably like something you would hear on Monty Python or Fawlty Towers).  Most people in the UK enjoy talking to visitors and will not make a big issue about different meanings of certain words. But if you are making a big gaff in pronouncing place names you may gently be corrected if only to aid understanding.

Only a very rude person or someone 'taking the p*ss' would make an issue of pronunciation to your face. If they do, either ignore them, or if you are feeling brave, fight back (verbally!) and engage in a bit of banter, you may even make a friend or two!