I never hated Trump for the first 30 or so years I knew who he was, before he became a politician. He was a boastful buffoon (as Philip Roth recently called him), but the way Spy magazine and Letterman mocked him he seemed harmless, and frankly Spy and Letterman were just about the only places I'd even encounter him back then. The racist strain already existed (the Central Park Five, for example) but for some reason it didn't stick in my mind.
Later there was The Apprentice. I never watched more than a couple minutes of it because it seemed so cheap and vulgar, a love letter to the cruelties of capitalism -- be selfish, be ruthless, deceive, backstab, grovel to whoever's above you, kick whoever's below you, and you too might one day have Trump's amazing life: firing schmucks willy-nilly, zipping around in limos, marrying ever-younger wives, defecating into a toilet made of 18-karat gold, etc. I didn't hate Trump then, not even close, but I felt repulsed both by him and the idea of an audience enjoying his show unironically.
For me, it was the birther garbage and the Mexicans are rapists/drug dealers speech when he crossed the line from harmless boastful buffoon to dangerous boastful buffoon. That's when I started hating him for real. And of course since then he's only given me more reasons to hate him. There's obviously still a lot of humor there (he's still a boastful buffoon, after all), but the ugly aspects of his personality now prevail.