'I do not want to give my bike to your spoiled child': Entitled Karen demands teen give his bike to her kid; teen holds his ground when Karen tries stealing it

In a busy apartment complex, a 14-year-old boy who loved riding his bike found himself in a weird situation. As he was cruising through the buildings, another kid spotted his bike and immediately wanted it. The other kid started out with an innocent compliment, but things got worse when his entitled mom, who we'll call Karen (of course), showed up and demanded the teen give up his bike because her son was younger. Lucky for the boy, an old man who caught the whole saga chimed in and told Karen to back off, reminding her that the OP had every right to keep his OWN bike. But Karen was stubborn and accused the teen of stealing the bike, even trying to take it by force. This understandably made the teen angry and drew a crowd as he yelled at Karen to back off and called her child spoiled. Despite the ordeal, the OP stood his ground and refused to give up his ride. 

What would you do in this situation?