The nTag sleep attack. The badges at Pop!Tech were wee interactive computers called nTags. When engaged in conversation with someone, you could choose to send your contact information to that person, see what that person is interested in (based on your interests), get recommendations on people that they have met that you should meet, and generally augment (or hamper) networking.
Many attendees liked them and used them happily, but others revolted. Some people started trading their badges with others. Early on during the conference, Whit Diffie hacked his nTag badge to send a sleep command to any nTag badge in range, effectively deactivating them. As word spread of the hack, people sought him out to sleep their hated badges. Others were pissed that he was turning off their badges without permission; someone asked at the end of the conference if sending a sleep command constituted an attack (When Sleep Attacks!). Following Diffie's lead, a woman hacked her badge to send the sleep command and a disgrunted Pop!Tech goer tried to rip her badge from around her neck (When Liberal Nerds Attack!).
I didn't particularly like my nTag badge (it was too heavy for one), but I can't argue that it didn't result in some interesting social behavior, though perhaps not the behavior that the nTag folks promised in facilitating networking. [kottke.org]