Ice cubes and tickle torture, are easy ways to get revenge, and keep him tied ud up longer than he had you.
Leave the blindfold off and taunt him as much as you can without actually doing anything, and that will make him more nervous.
look around your house for small things that you can use to torture him, such as anything that might get a reaction from tickling,
or something that might just bug him enough to beg from behind the gag.
Trust me, it's a lot of fun to see your friends struggling and squirming at your hands when they have no chance to escape.
But always remeber to keep things safe so no one gets hurt.