Right, there's nothing he/she can do. You don't even need to hide your stash, bro. The cops would need a warrant to search your house, so just deny any illegal actions, and do not allow anyone to enter your home. Threaten to call the cops on the guy if he does not leave, but don't call the cops.

It would be funny if you went through all this scared, and then found out it was something harmless . In fact, it usually is something harmless when shit like this happens, I noticed. I've been confronted with similar situations after smoking a bowl, and it scared me too. But there is nothing anybody can do--NOT EVEN THE COPS, unless they have a warrant!