1. Melky Cabrera
The only reason B.J. Upton isn't the most hated Brave in the last twenty years is because Melky Cabrera exists.
When the Braves acquired Cabrera, along with Mike Dunn and Arodys Vizcaino, they thought they getting a dependable, switch-hitting outfielder.
Instead, they got a "pudgy" player who wasn't interested in playing for the team. He'd have his worst season as a Brave, hitting .255/.317/.354 (77 wRC+) and playing horrible defense en route to a -1.5 fWAR season.
But, after being released following the 2010 season, Cabrera continued to torment Braves fans.
Not only did he immediately improve with the Royals the following season, he had the best season of his life with the Giants in 2012 (with some help from some PEDs).
When he visited the Braves in 2012 as a member of the Giants, his antics drew the ire of fans and players alike. He pretended to throw balls into the stands, taunted Jason Heyward, and had a crotch chop celebration gesture he pulled out multiple times. When Eric O'Flaherty brushed him back in the eight, it got a loud reaction from Braves fans.
"That’s Melky, and that’s why he’s not here anymore. He got a little happy when (Gregor) Blanco hit the home run. It won’t be forgotten.”"- Chipper Jones (AJC)
The silver lining of Cabrera's existence for Braves fans was his PED suspension. Not only was he cheating when he was playing Atlanta in 2012, but he was also drawing up a convoluted plan to get out of the suspension that dropped a month later.
In an attempt to persuade MLB of his "innocence," Cabrera created a fake website and a fake product to "prove" he didn't knowingly use PEDs. MLB didn't buy it, and his ploy was uncovered and revealed to the public. He allegedly spent $10,000 on the website.