You have your hands full. You have a young man on your hands who sounds like he is very good at keeping people off balance. You will find this in people who are off balance and out of control of themself.
Your step-son may be a "legal" adult, but he acts like an eight-year-old. You may not be his mother however, you are the reigning female authority in the house he lives in. You are within your right to demand being treated with respect. That goes for your husband too. He should insist his son treat his wife with respect.
With the others who have responded to you I must agree. Let the boy experience some "adult" treatment. He needs a job and to pay part of his living expenses while under your roof. The rest of what he makes he needs to hand over to you or his dad to be put away for him so he can eventually move out.
Without mutual respect there will be no rest or peace.
My prayers are with you,