This is an exclamation that you say when you're annoyed:
Jeez! Can we stop talking about your work and move on to some other topic please?
Sometimes you can also use it when you're surprised by something. For example, if someone walks up behind you and startles you, say this:
Jeez! You scared me!
"Jeez!" is short for "Jesus!" but you don't need to be Christian to say it. There may be some very strictly religious people who think it's wrong to say "Jeez!" or "Jesus!" when you're annoyed, but for the most part "Jeez!" is OK to say in any kind of situation - with friends, with coworkers, or even with people you don't know well.