Have the Last Word

This is a common and useful expression in spoken English.  It also describes a certain type of stubborn personality.  It’s not really a good quality, but it’s a character trait that many people have.

Taking Yourself Too Seriously

This is a great phrase to explain a certain type of negative psychology. If someone “takes themselves too seriously” it means they aren’t seeing  the humor with what they are doing.

I vs Me, Okay, etc.

http://www.merriam-webster.com/video/0041-i_vs_me.htm

http://www.merriam-webster.com/video/index.htm?&t=1343999768

Debating the Best Way to Learn a Language

I’ve Heard This Song and Dance Before

This is a long slang phrase but it’s a good one.  
 It’s easy to understand, remember, and actually use!

Slave Driver

If someone is a “slave driver” it means that they make
other people work incredibly hard.  No one likes a slave driver.
They are so difficult to work for and they don’t make your life happy.

hindsight is 20/20

If someone says, "hindsight is 20/20" they mean that it's really easy to see what you should have done when you look back. It's just impossible