For Example : "My throat is finally feeling better, knock on wood!"

or

"I'm so happy it hasn't rained yet, knock on wood"

"I am going to the mall to look for some trade"
"The club was packed with trade, honey"

(made-up scene from GTA San Andreas)

(at the beach)

Kent Paul: (ogling a hot girl come out of the water) Oi Maccer, just take a look at what just breezed out of the blue. That height, that arse, those jugs, those curves! Blimey if I'd be given the chance now I'd get to chuck my junk in that, knock on wood!
Maccer: Indeed man! Knock on wood, eh. Well alright then! *starts masturbating*
Kent Paul: No, jack-off Jimmy, not... ohh, *mumbles* fucking Northeners!

----------------
Mark H. Proud Urban Dictionary slang author since February 2004.

This chick is hot. I gotta knock on wood really quick.

The definition of knock on wood is pretty straightforward.

crogi: "ouch! i hurt my hand knocking on that wood. it looks like i'm bleeding"
bob: "want a cool glow in the dark harry potter band aid??"
crogi: "SA-WEET!"

in karate we like to knock on wood!