That’s what a 17-year-old named Adrian and his friends were planning for his birthday — a “kickback,” or a casual get-together on Huntington Beach. But once TikTok got hold of the invitation to the beachside, fire-lit party, the kickback devolved into a massive mob of partygoers, some of whom set off fireworks in the streets of southern California or got arrested for unlawful assembly. In other words — it was the stuff of not-quite-post-pandemic party legend. “Adrian’s kickback,” a hashtag