Wishy washy people can be like a roller coaster ride--when the times are good with them, it can be really good and when things are bad you just want to pull your hair out. Making a final decision might never happens when you're dealing with the fickle. Here are some ways you can reach out to them if you have the paitence to do so.
Take most of what they say lightly. Most wishy washy folks (also known as inconsistent) can't keep a promise if their life depended on it.
Sit down and have a serious talk about why they behave in a certain way. Some of their problems can go back to childhood-- the people they count on the most never could be at reach. It could stem from being from an unstable environment for them to act this way around people.
Be straight forward. There can be one disappointment to the next when these type of folks let you down. Let's say you want to go to the movies or other places. They agreed to it the at the last minute cancel on you. You, on the other hand, is the type to make plan things in advance while they break off dates or hanging out as a friend. Confront them about this pattern and give it to them straight that you are frustrated with their indecisiveness. If necessary tell them it is putting a danger to your relationship. This could possibly straighten up their act.
Play their game. People will never know about their own huge flaws unless they see it with their own eyes. Give the person the taste of their own medicine by becoming unreliable and undependable. When they plan something, cancel at the last minute. Or for example, say that you are going to help them move and call them up to say you can't help and other things got in the way. Do this at least five times and more likely they will be irritated and frustration by your 'inconsistent' ways. They will know how it feels when one do such things.