LOL a mate of mine does that to me all the freaking time. I always say sushi because I just know she'll go 'Ewww not that sticky rice crap!'
She hates rice for some unknown reason and yet will happily eat rice crackers, go figure. Same thing with movies, she'll say 'I'll watch whatever you guys (other friends + me) want to watch.' Of course, she'll then shoot down usually all of our suggestions, because she likes romantic comedies, a lot. The rest of us...yeah.
Sometimes I wonder why we're friends with her, but it's really just preferences. When I think about it, she's probably the most reliable and trustworthy person I've ever met.