The expression is usually, "You could have knocked me over with a feather!" It means, I was so surprised (and distracted or disabled) that I could have been easily knocked over with a feather. In other words, my defenses were way down, or non-existant so almost anything could have knocked me down.
you are exited
You could of knocked me over with a feather is an old saying. This saying means, whatever was said or done, is so surprising.
that your very happy
Great surprise :0
This isn't an idiom because you can figure it out if you look up the word "pins." It is a SLANG term meaning legs, so you knocked him over.
The phrase "you could have knocked me over with a feather" means that you were very surprised. A person who is so surprised that they are a bit disoriented might feel like something as light as a feather could be enough to knock them over.
I'm very happy and excited
It means that you were so surprised or otherwise emotionally shaken that you had trouble standing up -- so much trouble that it would have taken only the weight of a feather to knock you down.
Over there.
This is not an idiom. "It's over" means that it is over, or finished, or done. Whatever "it" refers to has concluded.
Over a Barrel: helpless, at a disadvantage
It's not an idiom because it means just what it seems to mean. You should stay on the side of the fence that you are currently on and not climb over.