Most authors of topics like these suggest you pull the co=worker aside and ask them way they did that. If depends on their reaction how you move on with the situation. If you have no proof, you should move on and either make better records of your ideas for later proof or be more vocal in meetings. I would only share ideas with people I trust or no one at all. This rough question to answer. Sometimes you have to move one and be better prepared next time.

well..its feels unfair really..but if it is a work team we cant avoid such situation..but if it concerns about competion at work well for me I will really confront the person who stole it and I will provide evidence that that's my idea i will prove its mine no matter what..I just dont want my work to become nonsense at all because i tried hard for it..

i will be angry i hate this i will embarrass him/her not forget or forgive villainous people if he don't confess

if this situation happened on me i would feel sad! first,i will ask he or she why stole my idea alone.if she or he has the special reason not just for his or her profite i think i will forgive him or her one time.if it happened more than one time i think i will not belive him or her any more and it reflect he or she is not the true friend or a bad co=worker.then i will take some steps,for example to collect some evidences to disclose.

If so I think the idea didn't come from him after all.The meaning of the idea maybe he don't konw.So maybe I just do nothing proved by time or I can come from a better idea. And if we are friends I should tell him or he will make mistake again.