This is the action of a defenseman in a basketball match that blocks somebody's shot in a manner in which they hit the ball into the backboard, and slide it off the edge of the glass.
Originally, the term was used in the popular video game NBA Street, but now it has been adapted into common vernacular on the blacktop.
Typically, the defenseman performing the windexing attains a large amount of street credibility for his action. The opposite happens for the other player.
Why is Alfred crying?
Oh, Tyrone just windexed his shit into the third row.
Oh snap; that's ultimate dishonor.