Sounds like you got Zuckerburged. Everyone is giving genuinely sweet advice but no one other than one or two people are being realistic. If you work in private industry, your coworker is your competition for titles and raises. The more good ideas they are credited with, the better they look to management, right?

In this type of environment, the person who says it first for all to hear gets the kudos. Why would you show your cards to the other players before the game starts?

Chalk it up to the game and keep churning ideas. Don't be delusional and think of they misunderstood me blah blah blah. You know what happened. You told your idea to someone you trusted and they ran with it to get the credit. Better luck next time.