I love Vocaloid. Yes, the annoyingly high-pitched "robots" that sing unprofessional J-POP and sound like auto-tuned children. About 60% of my iPod is taken up by Vocaloid songs, and everybody berates me for it. I don't find the voices too grating (usually), I know where to find the high-quality songs, and I think the characters are cute. Apparently, that's grounds for being made fun of constantly. People also seem to think that since it's not actually a human singing, no effort or talent whatsoever goes into the singing. In fact, making a Vocaloid sing well takes just as much effort as actually singing! Producers spend countless hours perfecting pitch and tempo and everything, much like a singer spends that time perfecting their voice. But no. The end product isn't human singing, therefore it's impossible that somebody could have had to try to make the song sound good. It's all just the computer.
Also, DragonForce. Everybody hates DragonForce. People go on about how they sound too similar all the time, and they're incredibly cheesy. Also, so many people have decided that they play the songs slowly and speed them up after, it's practically true just because they say so! Honestly, I couldn't care less about whether or not they speed up their songs, or if their songs all sound the same, or if the lyrics are about fighting dragons with the power of friendship or whatever the hell they sing about. I think the music sounds cool. Therefore, I listen to the music. Nobody seems to understand that, and they make fun of me just for listening to Black Fire or Operation Ground and Pound once in a while.
I listen to more bands that have a bad reputation, but I can't think of them right now.