Why did the patient do so without Dr House committing any error ?
MR FUNSTEN: Doctor House ...?
HOUSE: Hey! Mr. Funsten! I was wondering when you'd be back. You've got some papers for me?
MR FUNSTEN: You've caused me considerable mental distress.
HOUSE: I certainly hope so.
<Mr. Funsten passes a manila envelope containing some legal papers to House.>
HOUSE: What? Too cheap to get your lawyer to serve it for you or is it just more fun this way?
Funsten is a 'slip-and-fall guy', someone who fakes an injury to initiate a lawsuit that he hopes gets quickly settled out of court. Dr. House recognized this pattern of behavior from his medical records earlier at the clinic and was half expecting Funsten to show up at some time after the clinic visit. Funsten now seems to be claiming 'mental duress' due to the care he received from Dr. House.
"You've caused me considerable mental distress."
Secondly, why did he want to take away the papers from Dr House and why didn’t Dr House hand them back to the patient ?
MR FUNSTEN: I'm obviously prepared to consider a settlement.
HOUSE: You've got gonorrhea.
MR FUNSTEN: No I don't!
HOUSE: Well, maybe you're right but I have the lab results that say you do. Could be a false positive and normally I'd run a second test but since you're here I'll just go with the first.
MR FUNSTEN: You're just trying to scare me.
HOUSE: It's reportable you know. Public health issue.
MR FUNSTEN: Well, I'll be sure to let my wife know.
HOUSE: Oh, don't bother yourself. The state will call for you. Look, if you're clean, I'm sure it'll all blow over. No big deal. But there's an easy way to find out. Get one of your doctors to run a test.
<Mr. Funsten tries and fails to snatch the manila folder back from House.>
HOUSE: Uh-uh. These are mine now! I'll see you in court.
Mr. Funsten had driven 70 miles out of his way to seek medical care away from his hometown of Maplewood, New Jersey because he had a habit of suing doctors and no one closer would treat him anymore. Dr. House essentially blackmailed Funsten into dropping the lawsuit by intimating that he would publicly reveal Funsten had gonorrhea (which he likely did not). Additionally, House kept his copy of the court documents in case Funsten decided to change his mind. The legal papers of a dropped lawsuit might also benefit the next doctor down the road that Funsten decides to frivolously sue.
"Uh-uh. These are mine now!"