“The last straw” is used to refer to the final difficult event that happens after a whole series of difficult events. For example, if you are having a bad day, finding out you failed a test might be “the last straw” that causes you to break down and express anger or frustration. The phrase is a variant of an older expression: “the straw that broke the camel’s back,” from a time when camels would carry loads of straw. While camels can carry very heavy burdens, there’s a limit to what they can handle.
When Americans say “Let’s call it a day,” they don’t pick up the phone and call someone named “Itaday.” Instead, they mean that they will stop working for the day.
When Americans say, “Hang in there,” they are encouraging you to continue to try to do something even though it’s difficult. This expression is usually meant as an encouragement. For example, you might tell your friend, “Hang in there! Even though you have four tests tomorrow, things will work out.”
* This video is one of a series explaining popular American idioms. The videos, designed to help international students understand conversational English, are produced by the University Writing Center at Texas A&M.