"It's late and you've accomplished a lot. Why don't you call it a day?"
can't make heads or tails of something: can't understand something at all;
find something confusing and illogical.
"I can't make heads or tails of your e-mail. Were you having problems
with your computer?"
catch one's eye: attract one's attention/interest.
"This brochure about Tahiti caught my eye when I was at the travel agency."
catch some Zs: sleep for a while; take a nap.
"You look tired, Dave. Why don't you catch some Zs?"
change one's mind: decide to do something different from what had been decided earlier.
A: "Why are you working this week? I thought you were going to be on vacation."
B: "I changed my mind. I'm taking my vacation next month."
chicken (adjective or noun): cowardly.
"Fred will never ask Lucy for a date. He's chicken / a chicken.
"How's the chow in the university cafeteria?"
chow down: eat.
"It's almost 6:00. Are you ready to chow down?"
a cinch: something that's very easy to do.
A: How was the test?
B: It was a cinch. I finished it quickly and I know that all my answers were correct."
cool (also kewl): neat, special, wonderful.
"The ESL Cafe on the Web is really cool!"
Cool it!: calm down.
"There's no need to be so upset. Just cool it!"
cost (someone) an arm and a leg: cost a lot; be very expensive.
A: "Your new car is really nice."
B: "It should be. It cost (me) an arm and a leg!"
couch potato: someone who spends too much time watching TV.
"You're a real couch potato, Jay. You need to get more exercise!"
cram: try to learn as much as possible in a very short time.
"Sidney did well on the test because he crammed for it. However, he probably
won't remember any of the information a couple of days from now."
crash course: short course designed to give a lot of knowledge/information in a very short time.
"Tom's company is sending him to a business meeting in Istanbul.
Should he take a crash course in Turkish?"
Cut it out!: stop doing something (that's annoying).
"You kids are making too much noise. Cut it out!"