Venetian Blind Cord - Auto Tightens

Find a position to lie on your back below some Venetian blinds. Pull the blinds all the way up and place in locked position. Tie the cord around your balls. Start jerking off slowly. Release the lock on the blinds so that they start to descend. This will pull the cord tight. As you jerk off start to hump your hips up. This will lower the blinds slightly and when you hips come back down the cord will be that much tighter each time. Eventually you will not be able to comfortably lower yourself all the way down and you will come with a very tight cord around your balls.