The Indecisive person
There's probably someone in your office who fits into this category - the vague and indecisive person. The ones who can never which part of the project they want to do, which clients to pitch for or even where to go for lunch.
They can be seriously frustrating, especially when you end up having to make all their decisions for them!
It's OK when it's just a little decision - like do they want tea or coffee - but what about big decisions, like how to put across a pitch? If they leave the decision to you and your approach fails, the blame falls with you, and that just isn't fair.
How to deal with an indecisive person
First of all, do all you can to get a decision out of them. Present them with the scenario, like "We could split up the task like this, or this, which would you prefer?" If you ask them a direct question, they have to give you a direct answer.
If they do reply with the classic "I'll leave it to you" then let them know that if they really can't decide, then say you're taking their response to mean they agree with you. That way the responsibility falls on both of you if it goes wrong!