Okay, so this word is so horrendous that I actually didn't want to write it out loud in this thread but here goes:
Brainfart
This word showers me with so much disgust every time I hear it that I don't know what to do. It's so obscene. I mean, your brain can't fart, but the word forces me to imagine a smelly fart bubbling up from the brain. Where does it go out? Probably through the ears, but what if it escapes through the nostrils?! Or what if you feel that weird pressure behind your eyes and you can feel the fart-bubble pressing itself out through the sides of your eyes?
So if there is actually a word I hate then it's that word.