The UK is documented to have one the widest and most exhaustive slang vocabularies in the world. Here are a number of phrases that could very possibly confuse native English speakers from other English speaking countries such as Australia, The USA, Canada, South Africa etc. These phrases might not be so much help in the official exams but they are very common in British English and using some of them might help you to sound like a real British native.
1. Chuffed (adj) To be very pleased about something.
e.g. Bill was chuffed that he had run a personal best in the 10KM that morning.
2. Fortnight (noun) A period of 2 weeks.
e.g. Next week I won´t be able to come so I will see you in a fortnight instead.
3. Gutted (adj) To be extremely disappointed about something.
e.g. Jerry was gutted that Paula turned down his proposal.
4. Miffed (adj) To be upset about something
e.g. I´m a bit miffed not to be invited to John´s wedding.
5. Manky (adj) Dirty and unpleasant
e.g. The matress was so manky after my last tenant moved out.
6. Quid (noun) A synonym for a pound.
e.g. Can you lend me a quid? I forgot my purse.
7. Grub (noun) A synonym of food.
e.g.I´m so hungry. Let´s go to KFC and get some grub.
8.Pain in the Neck (noun) Something or someone annoying.
e.g. My sister is such a pain in the neck. I wish she would leave us alone.
9. Knackered (adj) Someone that is very tired
e.g. I´m absolutely knackered. I have been awake since 3 in the morning.
10. Fag (noun) A synonym of cigarette
e.g. I´m just nipping outside for a fag. I´ll be back in 5 minutes.
11. Fluke (verb/noun) Something caused by luck or chance.
e.g. The goal from Ramos was a fluke. There is no chance he meant to do that.
12. Bloody (adv/adj) Used as an intensifier. Additionally it is used as a mild swear word.
e.g. English is a bloody hard language to bloody learn.
13. Bee´s Knees (adj) To say something is great.
e.g. This lasagna is the bee´s knees. I love it.
14. Skive (verb) To avoid doing something
e.g. Tom isn´t really ill, he is just skiving so he can avoid doing the exam.