I guess assertive is being direct and standing your ground. You dont have to "convience" or manuplate or force anything.... only to stand firm, be respectful of others and yourself, say it once and let it be.
Agressive to me is the person who pushes their opinions, gets into my space while doing it, will not let a subject go, angery, controling, manuplating. Doing what ever it takes to make it what they want.
My worst is the passive agressive.... I so struggle with that one.