To Tie the Knot

Meaning:  To get married

Hi Karla,

I hope you had a great vacation! A lot happened here while you were is Costa Rica!
Michelle went to Florida for a few days, Vini bought that car he wanted, and... what else? Ah, guess what?! Lina and John tied the knot last week!
I am so happy for them. I saw some pictures and they looked fabulous.
Well, I hope to see you soon and hear all about your trip! Call me when you have a chance.

Sylvia

https://languagesystems.edu/

Kadult

Melissa: I’m trying to get Jon to move in with me, but he says he prefers living
with you as a roommate.
Aaron: It’s great living with Jon. It’s like we never left college.
Melissa: You guys are such Kadults. When are you going to grow up. That’s why you don’t have a girlfriend.
Aaron: Blame our parents, they loved us too much.
Melissa: You guys need to become men. Playing video games all day is so
childish.

Kadult means you are a grown adult, but still act like a kid (child)

https://languagesystems.edu/

Ball in (your) Court (used as an expression)

Meaning:
The expression, “the ball’s in (your) court,” is typically used to express that it is now the other person’s turn to commit to the next move.  This expression comes from the game of tennis, where it is now the opponent’s turn to perform the next action.  This is usually a follow-up expression where the first person had already initiated the first action and it is now the other person's turn to react to it.

Situation 1:
“The salesman provided the customer with all of the information and details about the product and also offered him a great discount as well.  The ball is now in the customer’s court to decide if he wants to buy it or not.”

Situation 2:
Mary:     “My boyfriend and I have been together for about 10 years now and I think I’m ready to take it to the next level.  We both have good jobs now and we both still love each other very much.”
Lisa:    “Have you tried asking him if he wants to start a family together?”
Mary:    “I did and he said he needed a bit more time to think about it.”
Lisa:    “Okay, then it sounds like the ball is in his court now.”

https://languagesystems.edu/

Tag along

Tag along (used as a verb, adjective or noun)

Situation #1: Two friends

Kate: I'm so excited. I'm going to check out that new horror movie!

Chris: Really? I've been wanting to see that. Mind if I tag along?

Kate: Not at all! Let's go!

Explanation: "Tag along" means to go with someone. When used as a verb, it's usually asked in a question (as in the above example, or if Kate had asked "Would you like to tag along?"). However, when used as an adjective or noun, "tag along" (or sometimes "tagalong" or "tag-along") is usually more negative, suggesting that the person is following another in a constant and possibly annoying way, as seen in the next example:

Situation #2: Two friends

Brie: Have you seen Valerie?

Kim: No, why?

Brie: Well, I'm avoiding her. She is such a tagalong! She follows me everywhere, and it's getting annoying!

Kim:  She doesn't seem like she's that annoying.

Brie: She followed me into the bathroom earlier, even though she didn't have to go, and then she followed me to my class, even though her class was on the other side of the building! I don't need a tag-along friend!

Kim:  Uh...

Valerie:  Hey guys! What are you talking about?

https://languagesystems.edu/

Lit

Meaning: Fun or exciting

Dialogue #1: Karla and Trey are at a big house party in LA.
Trey: Hey, Karla! How's it going?
Karla: Oh, hi Trey. Great! How about you?
Trey: I'm good. Isn't this party lit?
Karla: Yes! I'm having so much fun!
Trey: Me, too. Tom's parties are always exciting.



Dialogue #2: Pam and Terry are talking about a new movie.
Pam: Have you seen the new James Bond movie?
Terry: Yes, I went last night. It was lit!!
Pam: Really? I haven't seen it yet, but I've heard it's awesome. I can't wait to go this weekend.


Explanation: The term lit has meant "drunk or intoxicated" for over a century. However, recently its meaning has changed to "exciting," as well as "excellent" or "awesome." In the first dialogue, Karla and Trey are talking about the party as being lit or really exciting. In dialogue #2, Terry tells Pam that the new James Bond movie is lit or awesome.

https://languagesystems.edu/

To hit the nail on the head

Context #1
Jill: I like John, but there is something a little strange about him.
Jane: Yeah, he always wears the same shirt.
Jill: You know what? That's it! You hit the nail on the head!

Context #2
Tom: People in Southern California drive so dangerously on the freeway. I wonder why?
Joe: Well, people could avoid a lot of accidents if they just used their turn signals when changing lanes.
Tom: Exactly! You hit the nail on the head!

Meaning: "to hit the nail on the head" is used when someone has an opinion or an idea and it is exactly right.

https://languagesystems.edu/

"To get something/someone out of someone's head"

Meaning: to stop thinking about something or someone


Example 1
Hey Lina, I love that song you played for me yesterday! What is it called?
I can't get it out of my head! I really want to add it to my playlist!
Let me know as soon as you get this text! This is driving me crazy!

Example 2 
John, I had a great time with you last week at the party. I know we are friends, but... I think about you all the time.
I think I am falling in love with you. I can't get you out of my head. Do you feel the same way?
I am so embarrassed to ask, but I need to know. ?? xoxo, Anne.

Notice that in both text messages Anne is having a hard time not thinking about something or someone.
In the first example, she is asking her friend to let her know the name of A SONG she can't GET OUT OF HER HEAD! She can't stop playing the song in her head.
In the second example, she is letting her friend know she can't stop thinking about him... She can't GET HIM OUT OF HER HEAD because she is probably in love with him! 

http://languagesystems.edu/