#1. Pink Floyd -- Syd Barrett
Syd Barrett was the original lead singer and guitarist for Pink Floyd, and by all accounts, he may well have been the most lip-wigglingly insane person to ever walk the planet Earth. He directed the band through its incredibly experimental stage in the 1960s, which is another way of saying he struggled to write music through the fog of acid in which he perpetually existed.
BBC/Strange Fruit Music
Despite this handicap, he was remarkably prolific.
Barrett already had undiagnosed mental problems, most likely schizophrenia, which he only made worse by eating tabs of LSD like Pez. He would routinely stand perfectly still on stage, repeatedly striking the same chord on his guitar for the entire performance, regardless of what song the band was actually supposed to be playing at the time. Other times he would stand with his back to the audience, staring at the amplifiers like he was on a vision quest to count all of the wasps flying out of them, and not play a single note. It got so bad that the band had to hire another guitarist just to fill in for Barrett when he was too out of his mind to perform, which tended to be most of the time. As his behavior moved from erratic to completely unreliable, Pink Floyd hired David Gilmour (who would eventually become Barrett's replacement) to play guitar while Barrett just kind of wandered around the stage like a deaf guy at a Greyhound station, if he showed up at all.
Since Barrett had written all their songs up to that point, the band was reluctant to give him the boot entirely (unlike certain Gin Blossoms who will remain nameless), so they tried to keep him around as a non-touring member. He apparently resented the ever-loving shit out of this, because on the very last practice session he attended, he presented the band with a new song called "Have You Got It Yet?" which consisted of him playing the song, the band doing their best to replicate it, and him patiently correcting them by playing an entirely different song while singing "Have you got it yet?" The band reportedly repeated this process a handful of times before realizing they were being trolled and kicking Barrett the hell out.
"See, have you got the joke yet, is what I'm asking. The joke being you guys are assholes."
For several months after, he would show up in the front row at Pink Floyd shows just to stare at his replacement, Gilmour, like he was trying to melt Gilmour's skeleton with his mind, which is quite possibly exactly what he was attempting to do.
Here he is trying the same technique on Dick Clark.
After Roger Waters, the bass player, took over lead singing and songwriting duties for Pink Floyd, the band's output switched to atmospheric songs about depression, death, and existentialism, which was apparently just what kids in the 1970s were yearning for after The Beatles broke up. They actually wrote a few songs about Barrett, too, including the appropriately titled "Wish You Were Here" and "Shine on You Crazy Diamond," which seem to send conflicting messages. He actually showed up, unannounced and uninvited (though completely welcome), during the recording of the latter, having shaved off his hair and eyebrows and gained the weight of an extra person, because being crazy will transform you into a WWE mascot. And that was it -- with the exception of Waters (who ran into him once more, in a chance encounter on the street), nobody in Pink Floyd ever saw Barrett again. In fact, virtually no other living soul ever saw him again. It's like he went to live in TRON with Jeff Bridges.
The only reason anyone ever heard of Pink Floyd is because they kicked Barrett out of the band, and the only reason anyone ever heard of Barrett is because he got kicked out of Pink Floyd. That's the kind of relationship I want with my friends.
For more rock star insults, check out 5 People Cheated Out of the Rock and Roll Hall of Fame and 5 Absurd Reasons Musicians Have Been Fired From Famous Bands.