Mike Isaac’s Super Pumped describes Kalanick’s attempt to “cripple” Lyft, including by disrupting Lyft marketing events:
He’d send his own employees to the [Lyft] events, where they would show up in jet black T-shirts–Uber’s signature color–carrying plates filled with cookies, each with the word “Uber” written in icing. Each Uber employee had a referral code printed on the back of their T-shirt. The codes were for Lyft drivers to enter when they signed up for Uber, earning them a bonus.
(p.122)