slapp'nin
Both words shakin' and happnin', conveniently wrapped into one word. Both words alone have gone out long ago, but slapp'nin brings it all back in style.
Yo dude, what's slapp'nin!
Dude #1 - hey, what's goin' on?
Dude #2 - what's slappin' man!
Dude #1 - hey, what's goin' on?
Dude #2 - what's slappin' man!