be at (someone or something)

be at (someone or something)

1. To be located in a particular place. Where are you at? I just looked inside the restaurant, but I didn't see you. I'm at the main entrance—where are you?
2. To occur at a specific time. According to the tickets, the concert is at 8:00, but I'm sure the headliner won't go on that early.
3. To nag or pester someone to do something. My mom is always at me about cleaning my room—it's so annoying.
4. To be working on something determinedly or persistently. I've been at this problem for hours and still haven't found a solution.

be at it

1. To partake in an action, activity, or pursuit vigorously, exhaustively, or determinedly. I studied really hard for this test; I was at it all night. I wish those dogs would quit barking, they've been at it since the sun came up!
2. slang To be engaging in sex. I can always hear when the neighbors are at it. It's really embarrassing!
Farlex Dictionary of Idioms.

be ˈat it

(informal)
1 be talking or arguing too much: It’s time you two stopped arguing — you’ve been at it all morning!
2 be having sex with somebody
Farlex Partner Idioms Dictionary

be at

v.
1. To be located somewhere: The hotel is at the center of town. I am at the corner of 11th Street and Third Avenue.
2. To take place at some given time: Our meeting is at noon. The movie is at 8:00, so we've got plenty of time for dinner.
3. To be busy trying to accomplish something; keep at. Often used with it: I have been at this interminable project for weeks now.
4. To remind someone regularly about something or to do something: He's been at me about the book he lent to me.
The American Heritage® Dictionary of Phrasal Verbs.
See also:
  • be at
  • be at it
  • dine at
  • dine at (some place)
  • a hot spot
  • back door
  • hole in the wall
  • at a sitting
  • Eat at Joe's
  • invite (one or oneself) over (for something)