a good friend of mine is considered a party dude by his co-workers. he made one little joke about having his age in drinks for his birthday and it's followed him around the office. he rarely drinks or goes to parties. but whenever alcohol, bars, or partying is mentioned now, they look over at him.
another example: i like to invest and research the stock market. one time, at the office, someone was asking me about stock recommendations. i mentioned that i sometimes use options as well as buying stocks. now, somehow, i'm labeled as a "short seller" and partially responsible for the current bear market. it's in jest, of course, but it's kinda annoying. not to mention factually untrue. someone even forwarded me an article about the dangers of short selling.
it reminds me of that game we once did in grade school, where you tell the first person something and then they whisper it in the ear of the person next to them. by the time you get to the last person, the message is all screwed up.