If someone were to say they had an "Ultra Mega Neon Fly-Ride Best Friend" it would mean that the two were beyond friends, even beyond best friends. It would mean that these to people like each other. In other words, these people are sus. Ultra Mega Neon Fly-Ride Best Friends are typically of the same gender and usually two boys. However, they could be two people of another gender as well.
Guy #1: "Man, Zach and Jesus used to be Ultra Mega Neon Fly-Ride Best Friends, I don't know what happened."
Guy #2: "Yeah bro, I don't know. But, Krystoff and Avery are Ultra Mega Neon Fly-Ride Best Friends, Just a little less recently."