be at it

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 engage in sexual intercourse. I can always hear when the neighbors are at it. It's really embarrassing!

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