When you point a camera at human, 99% of the time that person will strike a pose of some kind. These "poses" are absurd and the longer that these "poses" are held, the more ridiculous and hilarious they get. So why not shoot video and make your subjects wait and wait and wait.
We live in a magical time. Still and video cameras are one in the same. You're point and shoot, DSLR, or cellphone will work perfectly for this "trick." I personally enjoy the woman's tactic in the video above; get your subject make a crazy face and then keep saying "tell me when."
Check out the videos below for a few different options.
The snapchat one is so hilarious!!
HaHa a portrait wouldn't be a portrait without the tongue sticking out and rolled eyes.
At work we have to take new starters portraits. We have one of those fold down background/softboxes so before they subject turns up, one of my colleagues climbs inside the back ground and after a 1-2-3 count down we give em a scare. Might have to start filming them.