The American Association of Retired Persons (AARP) published (October 2008, AARP Bulletin) a list of 50 words that every 50+year-old should know in order to be able to comprehend their children and grandchildren. I've discovered that, even in the workplace, there can be a generation gap between senior-aged instructors and the twenty- and thirty-something teachers.
My first taste of this was last year when a younger instructor joked that I was probably a 'cougar.' Curiously, this word was also listed by AARP as an expression seniors should know. Is this a reflection of the times? Demi Moore and Ashton Kutcher.
Some of the other expressions to make the list are crackberry, google, vlog, webisode, and wikidemia. Some common acronyms used in textmessaging are BFF, IDK, LOL, OMG, ROFL, and TMI. If you've got fashion-conscious young relatives, you should know bling, tatted out, tramp stamp, scooby doos, and soul patch. If someone young is (or you're) into 'love,' you should know what baby mama, cougar, cupcaking, and flirtationship mean. Your peeps are your closest friends or your family, and then there are brodowns, bromances, a frenemy, and nOObs.
When it comes to music, there's crunk and emo plus disco naps and mashing up. It used to be that checking vitals was what the doctor does, but it now applies to checking your electronic devices. Do you floss, friend, jump the shark, rock, or talk smack?
If you really like to be emphatic, you can say it's fo'shizzle, obvi, and totes. And if you're looking for some colorful language, how about the bomb, off the chain, ridonkulous, sick, tight, and wack?
From the British Isles, you have chav, nutter, snog, and T5, and that brings us to the last word on AARP's list, a word for a great-looking (-shaking) butt - a badonkadonk.
You may not want to use these expressions in your own speech - risking misuse, but understanding them may be a worthwhile endeavor.