LOL. I run into this problem more than I would like to, and I admit it is partially my fault.
I pick my words carefully when I communicate, and people often misundertand, or assume that there is a misunderstanding. I tend to be very direct with people, and it seems that people dont expect that at all.

For instance some annoying man in the doctors office sat next to me, and started trying to strike up a conversation, and I simply said in plain words that I dont want to talk to you. Thats a very clear statement. He laughed as if it was a joke, ,and kept up his one-way conversation as if I was joking. Grrrrrrr!
What I find more annoying is when people ignore your 1st response. If I say no I mean no, and I dont like to have to keep repeating it. If I say maybe I will think about dont hound me for an answer. Most people are not very direct so I guess it throws them when others are? I dont know.