My Google Kung Fu is strong so I will manage . I may add a bunch here anyways. One that stumped me until I finally looked it up was "DA" Density Altitude.
I'll play along:
YMMV= Your Mileage May Vary - meaning you may get different results
WTF= What the Fuck - self explanatory
SBO= Shit'll Buff Out- just made this one up. It's usually spelled out and used sarcastically.
IBTL= In Before the Lock - not so much here but in other forums, people behaving badly can cause threads to become locked by the Mods...
FPC=Flat Plane Crank