My DH and I like to blindfold each other for surprises and presents; usually something nice comes at the end of it, but this lends itself to occasional pranking. I once blindfolded him, told him not to peep under any circumstances, put some music on, and I left the house as quietly as I could. Some time later, I rang the doorbell. But he was good, he didn't move from his post, although he did call out for me. More than an hour later, I returned, and he was still obediently there! He was a bit miffed there wasn't a present or a surprise at the end of it, and that he'd been had!
When he blindfolded me for wrapping my presents in front of me (one of our favourite rituals), I once memorised as much as I could about the room first, telling him that he'd done a poor job of covering my eyes, and telling him about lots of things I could see. It didn't take him long to rumble me though, and he made me wait longer than usual!
I've done the trick on my nephew of "hand co-ordination": getting him to move his hands back and forth between mine, without touching them; then challenging him to do it blindfolded, and sneaking away while he couldn't see. He kept going for at least seven minutes!
My DH and I went to a lot of trouble to convince our Harry-Potter mad niece that she could Apparate (disappear and instantly appear somewhere else, for you Muggles out there!
). We stood her in a place where she could see both ends of the garden. At one end, there was a stool for her to stand on, and we told her she would jump off and finish at the other end, pointing out where it would be. I blindfolded her (International Statute of Secrecy), spun her round and led her to what she thought was the start. But I actually led her to just before the finish, where he had quietly moved the stool, got her to stand on it, then told her to jump off (destination, determination, deliberation). As he warned her not to peep or she might get Splinched, I quickly and stealthily returned the stool to its original position, then he turned her to face the start, and took off her blindfold. Her face was a picture, she really believed it! (Daniel Radcliffe, learn, with your wooden acting!) We managed to do a it couple more times (not the same day) before she sussed it.