with it, to be/to get

be with it

1. slang To be alert and responsive. I'm sorry, I'm just not with it until I've had my coffee in the morning. You've got to be with it, people! We have a deadline here!
2. slang To be hip, fashionable, or in line with current trends. Her latest fashion line just isn't with it—it's not what today's teens want to wear.

get with it

slang To understand or be knowledgeable of modern times, especially as relates to the contemporary trends, ideas, or fashions. (Usually said as a jocular or sarcastic imperative.) Get with it, John, nobody wears their hat like that anymore! Lots of couples live together before they're married, Grandpa. Get with it!
See also: get
Farlex Dictionary of Idioms.

get with it

 
1. Inf. to modernize one's attitudes and behavior. Get with it, Martin. Go out and buy some new clothes! You really have to get with it, Ernie.
2. Inf. to hurry up and get busy; to be more industrious with something, Get with it; we've got a lot to do. Let's get with it. There's a lot of work to be done.
See also: get
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

get ˈwith it

(informal) become aware of the most recent ideas, developments, events, etc: You never seem to know what’s happening in the world around you. Time you got with it, Paul.
See also: get
Farlex Partner Idioms Dictionary

get with it

1. in. to modernize one’s attitudes and behavior. Get with it, Martin. Get real!
2. in. to hurry up and get busy; to be more industrious with something. Let’s get with it. There’s a lot of work to be done.
See also: get
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions

with it, to be/to get

To be (become) up-to-date, conversant with the latest style. This American slang expression originated during the 1920s, when it became associated with sex appeal (thanks to Elinor Glyn, author of a stream of popular fiction, and the movie star Clara Bow, the “It Girl”). Richard Condon used the cliché in The Manchurian Candidate (1959): “They are with it, Raymond. Believe me.”
See also: get
The Dictionary of Clichés by Christine Ammer
See also:
  • be more than (something)
  • be more than glad, ready, etc.
  • be pressed for time
  • a run on (something)
  • be pushed for time
  • address (one's) comments to (someone or something)
  • address comments or remarks to
  • a rush on (something)
  • address (one's) remarks to (someone or something)
  • be not cut out for something