I hear what you are saying

I know what you are trying to say

Example:

I hear what you are saying. That man is a real problem.

iffy

not good, not perfect

Example:

Your idea is a bit iffy. Have you thought about the cost?

I'm history

I'm leaving

Example:

Great! Six 'o' clock. I'm history. See you Monday.

I'm not kidding

I'm telling the truth

Example:

....And then he hit the policeman. I'm not kidding.

in

in fashion

Example:

Palm computers are in at the moment.