Here is an interesting T-shit from ThinkGeek. The Locked ON Proximity Sensing shirt is a glowing animated T-Shirt that can detect another Locked ON shirt nearby. When two shirts are within a few meters of each other the glowing radar stops scanning and locks on.
The black T-Shirt are of 100% cotton. The animated decal can be removable for easy washing and the battery pack is concealed in a small pocket in side the shirt. Each Locked ON tee is priced at $19.99.