Pulling someone’s leg: This just means that you are messing or kidding around with someone. Not really sure the origin of it but it is a way to just say you are messing around.

Horse around: This definition is similar to “messing around”. A group of teenagers knocking over trash cans for fun would be an example of horsing around. You’re just having fun.

Jump the gun: This is also one that I am not sure of the origin of but it is one I use regularly. It means basically that you were too early on something. For example, a sports reporter expecting a player to retire reports that the player retired before he actually did. It was expected and may have happened but the reporter still jumped the gun.

Fishy: Exactly the same thing as suspicious. “Something fishy is going on” means that you do not trust what is happening and you think that something bad or illegal is going on.

Bite the dust: This essentially means that situation is already done. For example, if you have a 72% in  a class and you need a 118% on the final in order to get an 80%, then you can bite the dust on that because that’s impossible.