Now it's time to use those rubber bands. Don't worry, it won't be painful. Yet.
Take one and put around your balls, then wrap it again to make it tight. Make sure it's snugged up nice and tight against your balls, make the skin around them stretch.
Give them a playful slap from the side.
Now the other side...
*giggles*
That hurt you? If you can't even take a couple light slaps I don't think your chances of cumming are very good.