Be a post whore!

[Clodfobble]

Yeah, the stepmom relationship is a sticky one, and your husband is the one you should have a talk with. He needs to fully support you in the things you need done in your house (i.e., if the stepson is an adult then he is a guest and needs to behave as one.) Setting his alarm clock when he's not home is incredibly irritating, and breaking it is an understandable reaction after the umpteenth time. Definitely do not buy him a new one. Have your husband let him know that his alarm clock will mysteriously disappear each time it happens from now on. When he slams the door in the middle of the night, make your husband get out of bed right then to go talk to him about it. His growing wrath over this situation will be enough to fix the stepson's behavior, I'm sure of it.