To firmly slap ones penis across another persons face i.e. to be either very manly or very homosexual.
"Dude! That little limp wristed faggot just thwacked me!"
One jock buddy says to another...
"WHOA! Billy's asleep, someone thwack him!"
to hit hard and percise. Usualy producing a THWACK sound.
With a "THWACK" the bamboo rod hit table.
To receive a hand job or blow job, and to not finish.
"Dude, she was thwacking me for an hour yesterday."
"How did you not finish bro?
Nikki thwacked her friend on the arm.
The sound made by the scrotum striking the belly of a women whilst making love doggy-style
The thwack sound echoed through the room as I reached satiation.
A firm thumb that a hard penis gives to a female (or male... depending on your taste), in any number of places.
Puedes THWACK tu SCHLONG en mi cara, por favor?
Translation: Can you THWACK your SCHLONG in my face, please?
Being under the influence of methamphetemines, particularly Ice.
My homie Dropkick left his dope on the coffee table....and his coffe table out in the yard because he was thwacked