The friendship bracelet
This common scam involves someone approaching you and starting to put a friendship bracelet on your wrist. Once they've successfully tied it on, they'll demand compensation for it. Since it's pretty much impossible to get it off your wrist, you'll feel obligated to pay for it and, if you don't, they'll cause a scene. There are different variations of this trick but they all follow the same premise - you touch it, you've bought it. Don't accept a "free" item or service from anyone as they will almost always demand payment after you accept.