for example you are in a hurry and also waiting for a friend at their house to come with you, but they are being too slow and you are getting mad at them because of this, so you might say loudly and almost angrily: come on man, what are you doing?
that's a situation where we use this expression or another one like this: "bi jonb baba la massab" meaning "come on man!"
this is a little offensive, though, be careful when you use it!
hope this helps!