with it, be

be with it

1. slang To be alert and responsive. I'm sorry, I'm just not with it before I've had my coffee. Get with it, people! We have a deadline here!
2. slang To be current, 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.

with it, be

Also, get with it. Be or become knowledgeable about the current or latest trends, fashions, or ideas, as in She just turned 60, but she's still very much with it, or Get with it, Dad, that kind of razor hasn't been made for years. [Slang; 1920s]