What is the most appropriate response to the following scenario …

You wake up to hear crashing and bashing in your apartment. You figure one of your flatmates is just drunk and ignore it. The bashing goes on for a while. You keep ignoring it. Then someone walks straight into your room (no knocking, just walks in), you realise you don’t know who it is, so you say “Hello? Who the fuck is that?”, to which the response from a mans voice says “Ahhh, I’m trying to get into that room” and they point towards your male flatmates bedroom. You then say “Get the fuck out of my room” to which they say “heyyy, chilll, I can’t get into the room can I can get in through (gestures towards your wall)”. At this point you realise the man is only wearing a pair of underpants. And you go on to say (more aggressively) “GET THE FUCK OUT NOWWWW!!”, at which point they disgruntedly leave your room. You then try to go back to sleep. But then you hear them talking to someone in another part of the house, and definitely not in the bedroom they were trying to get into, so you get up just in case he’s up to mischief and check on what’s happening.

You then find the mostly naked man standing in your female flatmates room talking to her. So you ask her if she knows him and she says “No. I have no idea who he is.”. So you demand he leaves, which he seems to object to, but you be more insistent, then he leaves the room. You then tell him to get out of the hallway to clear him out of her way, then ask him what he is doing and why is there, to which he says he is trying to get into the same room he pointed to before. You ask him why, and he says his friend is staying there. Then you ask him “which friend?”, but the name he says isn’t familiar. So you ask him why he is in the apartment and he says he knows one of the girls who lives there, so you ask him why he’s trying to get into a particular room, to which he says he knows the girl that lives in there (but it is of course a males room that he is pointing to). You then ask him exactly who it is that he knows in this apartment and he says he can’t remember the name of the person.

No one else appears to be home.

At this point, what is the most appropriate course of action?

(I actually had to deal with this scenario earlier this morning)