My youngest was like that just recently. At first it was really rough, because I would lose my patience and start yelling too. Then I found a book (forgot the name, but its around here somewhere so I'll look into it) that really helped me control my temper which was a big step. When she started mouthing off, first I would put her in the corner with some quiet toys and her blankie. When she was ready to say sorry, she could get out of the corner. If she threw a fit while in the corner, I would take away the toy. If she did it again, I would take away the blankie. If she continued, she would go into the back yard to blow off some steam. It took a while but it really paid off. Good luck!