Check out the Pulse Trick illusion from Brian Brushwood and Scam School. As a conversation starter, Brian shows you how to use two toothpicks to detect a pulse.
Effect: You are able to show your pulse using two toothpicks. No matter how hard they try, your friend cannot.
Method: hold a toothpick horizontally by pinching one end between your thumb and forefinger, and laying it across the fingernail of your middle finger. Pull down with your index finger, and push up against that toothpick with your middle fingernail.
Next, lay a second toothpick on the first, so it balances on the palm of your hand and rests on the first toothpick.
If you press down and slide the first toothpick along your fingernail, the small ridges in your fingernail will cause the second toothpick to bounce wildly, seemingly without cause. By timing these movements, you'll be able to convince your friend that your pulse is causing the toothpick to move.
Now here's the important part: keep doing the trick like it's no big deal, explain to them how they should position the toothpicks, and act only mildly interested when they complain that they can't get it to work... This will drive them nuts! If you're looking to keep a girl pestering you for help the rest of the night, this is the effect for you.