Sideburst
A combination of sidetracked and outburst, referring to a random off-topic outburst in a conversation.
Person 1: "...and that's how I broke my ankle."
Person 2: "Cheesecake!"
Person 1: "What?"
Person 2: "Sorry for the sideburst, I got a craving."
Person 2: "Cheesecake!"
Person 1: "What?"
Person 2: "Sorry for the sideburst, I got a craving."