break (one's) balls
1. vulgar slang To exert oneself to the utmost degree; to put forth the maximum amount of effort or strain. Because of the slang reference to testicles, it is usually (but not solely) said of or by a man. I've been breaking my balls trying to get the new software ready by the release date. Don't break your balls getting over here, there's no rush.
2. vulgar slang To harass, harangue, or pressure someone about something, especially for a lengthy period of time. The boss has been breaking our balls over the number of sales our department has made this quarter. Quit breaking my balls, I said I'd get it done.
3. vulgar slang To tease someone. Aw, come on, dude, I was just breaking your balls. No need to get upset about it.