To play dumb

Context #1

Tony: Did you take my book?

Jack: What are you talking about? I didn't see any book.

Tony: Don't play dumb. I know you took it.

Context #2

Grace: So did you ask your boyfriend about that text he got from that girl Chrissy.

Amanda: Yeah, but he played dumb and said that she probably texted the wrong number.

Grace: So you think he was lying?

Amanda: Yeah, I could tell by the look on his face.

Meaning: "to play dumb" is used when someone pretends like they don't know something, when they really do know!

http://languagesystems.edu/ 

To blow it

Context #1 

Jim: So how did you do on your driving test yesterday?

Harry: Oh man, I totally blew it!

Jim: What happened?

Harry: I accidentally ran through a stop sign, so I failed it.

 

Context #2 

Kathy: I have that big job interview later today.

Sara: Good luck!

Kathy: Thanks, but I'm so nervous! I hope I don't blow it

Sara: Relax. I'm sure you'll do fine.

Meaning: "to blow it" is used when someone makes a mistake that leads to failure.

http://languagesystems.edu/