There are several concerns you should have about letting Bruce Wayne stay at your house. First, from what I've heard, you better lock up your booze -- when he's in "devil-may-care" playboy mode, Bruce Wayne drinks so much his breath will hurt your liver. And when he's drunk, he can get plenty rude and ruin a perfectly good dinner party by kicking everyone out of your living room just because his butler called with some "urgent" message.
And if you have any female friends, you can just assume they'll all be spending a lot of time at your house while Bruce is visiting. A lot of time. Because Bruce splits his social time between an apparent experiment to see if in fact human males really do have an unlimited supply of sperm, and another experiment to see if suddenly shifting from crass womanizer to misunderstood, socially conscious philanthropist make it possible for one man to have sex with literally every woman he ever meets (note: do not invite your grandmother to visit while Bruce is staying with you).
However, none of that will compare to the more disturbing elements that will manifest in your basement. You can expect to find Bruce down there all night long, somber and brooding, and often whispering things to himself about his dead parents. It can be very disconcerting. Whether this is just a symptom of his insomnia (perhaps causing him to have hallucinations?) or PTSD that he's never bothered to treat (with anything other than liquor and sex, that is), I'm not sure.
But whatever the cause, you don't want to bump into him while he's wandering the dark in your basement mumbling about falling down a well as a child and then witnessing his parents' murders. And seriously, don't stick around if he starts talking about how his parents' died, no good will come of hearing the detailed way he likes to describe it, I promise you.
He also comes and goes all night long, which means he's stomping up and down the stairs to your basement and keeping you awake. And come morning, be ready to awaken to find him sleeping half the day and using up all of your Tylenol. You've never seen someone with such bad hangovers.
The idea that Bruce Wayne might be Batman is ludicrous. First of all, just look at all of that behavior listed above -- do drunken orgies, insomnia, and all-night partying sound like a vigilante to you? This poor slob's parents were gunned down right in front of him, and he's so traumatized by it he still talks about it incessantly. He's probably terrified at just the thought of muggers and guns, and you think he might spend every single night running around looking to find them?
Trust me, if Bruce Wayne is staying at your house, you've got plenty to worry about without some wild paranoia that he might dress up in tights and go around beating people up all night -- which in fact would be less screwed up than Bruce's actual behavior!
The upside would be that you don't have to worry about whether he will pay his share of rent and the bills (although he will probably flaunt his ability to pay and give you hell if you're late with your share), and his butler comes by constantly to check up on him, clean the house up, and bring messages (presumably from vineyards, saying "Dear Mr. Wayne, SLOW DOWN!").
All things considered, it comes down to whether you think tolerating all of his bad, weird behavior is worth the benefit of having a multi-billionaire sleeping on your couch. Because it's true that every time he's out and you check under the couch cushions, you'll find a few hundred dollars.
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