Kick him out. Change the locks. Get a restraining order if he won't leave you alone. As you say, he's 20.

'quit taking it personal'

I cannot state this strongly enough:
you are in danger.

This guy is:
slandering you,
making you physically uncomfortable,
living off you,
trying to get control of your home & other assets.

& he will get more aggressive, not less.

He's taking over your life & your assets as aggressively as any other predator, & he won't stop until he's destroyed your self-confidence & taken control of your money, home, & autos, & then he'll either change the locks & you'll be on the street, or he'll assault / attack /beat you.
or assault you & *then* throw you on the street.

He feels entitled to do whatever he wants, & you need to protect yourself;
'entitled' people can turn violent if crossed.

You want to make this between him & the police or the courts, not between him & you.

Colleenoz is absolutely right:

Change the locks *now*, & get that protective order.

He can get his things later, after you've boxed them up & set them outside or put them into a storage unit.

Do not let him inside that house, & if he comes to the house or your work or your son's school, call the police at once.

I wish you the best.

See an attorney and let him advise how to get him out of the house. Have an officer there when you tell him and his behavior when you do will let you know if you need a restraining order and the officer will be a witness.

I had a problem with a renter one time when they threatened to pour concrete down our drain line if we didn't get over there with the rent refund. I already knew they has trashed the place and had 5 kids instead of 2. The police officer asked about the location and told me where he would be waiting and for me to follow him. You should have seen the look on the guys face, it was priceless. The officer told him if anything happens to this woman, her family or any of her property I will come looking for you. Oh, the power of a man with a badge and a gun.

Before you can just throw him out, who does the house belong to? Also, if he has no one else and his dad just passed away, I think you need to have some compassion for him. All that said however, you can't just let him get away with what he's doing. Sounds like he's very confused. Where is his mom in all this? I feel for you, this is a difficult situation. Sit down with him, explain that he needs a job ASAP and that you think it's probably best that he get his own place. If there is money from his father's estate, I think you should help him get a place and get on his feet. After all, this was your husband's son and I'm sure he would want you to look after him to some extent, especially if there is no one else. If all else fails, then yes, do what others suggested and seek legal and police protection, but jeez, give him a chance first. He just lost his father.

Karen, it sounds like she has tried the rational approach already: "I have talked to him many times about these different situations but all he keeps telling me is quit taking it personal."

I have empathy for anyone who loses their father at a young age, but that does not mean you have to accept borderline psychotic behavior. I agree with your suggestion, if there is money available, help him get his own place and get on his feet...absolutely. But it really does sound as if she's given him more than a few changes to knock off the bad behavior.

But she really needs to get him out of there soon, she has a 13 yr old son who is her primary responsibility, no telling the effect all this is having on him. I have a 13 yr old son too, and I really worry about the long term effect of everything I am going thru with my 16 yr old daughter with some pretty severe mental health issues (anxieties, depression, self-harm, etc.).

He didn't save any money in the 2 years he has already lived with you rent free?
That fact alone..... out he goes.
Don't be a door mat.

Hugs, I am sorry, please get step son out of the house. NOW. If you have to, use an attorney.