Kewl. Pronounced coooo-el.
Don’t use those. Those are actually so retro, they’re cool again. In fact, perhaps you should use them and then tease the kids about how uncool *they * are when they don’t get it. It’d be hilarious when the recent catch-on of “the bee’s knees” comes around to them and see you’re cooler than them.
Oh wow, I’d forgotten that one. Did you also have its cousin, “beat feet”? “All right, this party sucks, let’s beat feet.”
What about “cool beans”? As in
Kid: I got a A on my paper today.
Dad: Cool beans!
Kid: (punches dad in the stomach) Don’t ever say that to me again. (storms off to room)
Be very careful with that one.
I booked. We would also “make like a hippie and blow this joint”, as in leave this place.
I would like to emphasize the previous comment about very slightly out of date expressions used with perfect elocution and perhaps air quotes.
“Yes, I would be very ‘jiggy’ with that.”
Talking to my son about five years ago (he was about ten), I said that something was “cool”, with the meaning of “good”.
Son (squirming): “Dad, don’t say that!”
Me: “Say what?”
Son: “‘Cool’ - only kids say that! Ugh! It’s embarrassing!!”
So, me being me, I told him the ‘ancient’ history of the term, including showing him my copy of the Miles Davis album ‘Birth Of The Cool’, which was recorded before even I was born, when dinosaurs roamed the Earth.
I can say what I like to him now. 
My kids are pretty much past being embarrassed by my slang usage, being in their early thirties and all–but I did pick up a veritable buttload of oddball current usage due to working in a call center with the very young and hep–mostly very white kids who want very much to be black. I really like doing the educated slang technique, example: “because THAT, my young friends, is indeed how I roll!” as well as the lolcat and haxxorz-sprach. Teh intarwebs b teh roxxorz, don’tcha know…
My alltime favorite headscratcher expression is “thrashin’ bastard pizza!” because absolutely nobody knows what the hell it means which makes it the perfect thing to say in any circumstance. I usually use it as a general term of approval, e.g. “Hey, I just did something cool” my response; “Thrashin’ bastard pizza, d00d!” Then I throw in a “w00t!” just for s&g’s… I rather pride myself on ironic slang usage. 
Make sure there are no black people around and then call them ‘my niggaz!’ When they get on your nerves put your hand up and tell them to talk to it. But do the whole phrase, “Talk to the hand cuz the face don’t understand.” Even better, put up your talk to the hand hand and make a screeching brake noise.
Tell them they are ‘to’ up from the flo’ up’ and that his girlfriend has ass for days and that she’s a ho fo’ sho’.
Oh, oh and put extra 'ed’s at the end of words that don’t need them. Say, “Boy, you sure are light-skinneded”
Anytime they tell you something good like they did great on a test, tell them “Gimmee Five” and then jerk your hand away as they try and use you fingers as a slow comb to the side of your head.
It’s also fun to find some of your favorite old arcade games online and show them to your tech-savvy teens. My favorite was Centipede . Also good- Frogger, Pac-Man, Asteroids, and the ultimate: Pong. I like to tell them how I had a Pong game when I was about 6 or 7, and how when I was their age it was like, totally awesome to go to the arcade with my friends.
The looks of horror on their little faces… priceless.
In my house, my husband and I really are the cool ones that use the latest slang, as well as some old school classic slang. My 8 year old daughter is the nerd that actually likes to pick up some slang from us.
I guess I should be embarrassed to admit to that, but somehow I’m not. I’m too busy being proud that my baby is a nerd. I always wanted to be one, but couldn’t grasp the math!
But I will play along. If you want to mess with your kids, start calling all the girls in their peer group, “Ma” or “Shorty”. Or maybe some Jamaican profanity will be a nice twist. Whenever you get the oportunity to say WTF, say “what the bloodclot*!?” instead.
**actually pronounced 'bumbaclod", but babysteps. Babysteps. *
What do you think would happen if you introduced your wife as “my baby Mama”?
My 5’9" wife aka Cyn always gets irritated if I refer to her as my “shortie”,
you can toss that in too.
Dis my baby mama and top shelf shortie…so don be dissin oner.
I was out shooting pool with Kid Kalhoun once and a guy came up and asked him if he “was hittin’ dat”…we both "eeeeeeew"d so loud they guy apologized and bought us drinks. It was da shizzle.
My homeboy hooked me up with these Slang Flash Cards last Christmas (Actually the second set, “Slang 2,” but I digress, dog) and they have transformed me from a common wanksta into a dope-ass pimp all hyphy to sling tha slang, know what I’m sayin’? Peace, radio.
“STOP!”…pause and wait until you’ve reached peak anticipation and expectation on their face…“Hammer time!”
Then start step dancing.
I just came across this comic. Apparently more parents are devious than one might think.
Something else that was really popular for a while, at least where I live, was to shorten decent to just dece.
“That CD is dece, yo!”
“Gimme some more of that pizza. It’s pretty dece.”
“How’d you do on the test?” “Dece, I think.”
Then you can start shortening other words and really mess with them.
“Dude, your shirt is dece!”
“Don’t be so redic.”
When asking a roudy young urban hooligan to settle down at the mall, I once said in the most monotone voice I could muster “Sir, you will need to chiggity check yourself well before you wreck yourself.”
I have also been known to ask people if they are “keeping it fresh and or real” (yes, you need to pronounce both the ‘and’ and the ‘or’).