John Funsten was the clinic patient in the episode Paternity who was going to sue House. He was portrayed by actor Alex Skuby.
Funsten came to the clinic with an abcess on his knee. House worked out that he had originally had a small pus filled sac, but had decided to try to relieve the pressure with something like a nail file, which only made it worse. Funsten tried to deny it at first, then admitted it. House offered Funsten a Vicodin for the pain which Funsten happily accepted.
House then looked at the patient file and realized that Funsten lived 70 miles away from Princeton. When Funsten didn't have a reason for being in Princeton, House surmised, correctly, that he wasn't allowed to go to any closer hospital, probably because he was in litigation with them. Funsten denied it, or that he wanted to sue House, but House started asking him inappropriate questions because that would help a malpractice case. Thinking House will also refuse to treat him, House tells him to stay put and that he will drain the pus and run lab tests to make sure it isn't anything serious.
House is dead on - Funsten returns almost immediately to serve a malpractice suit and House isn't surprised. He's also ready for him. He tells Funsten that he has gonorrhea and that House is duty bound to tell the state's medical officer of health. They will tell his wife so she can get tested. House says he would run another test, but he's not going to. He tells Funsten that since they're in litigation, he can't give him the test results, but it should be easy to prove he's clean - he just has to find another doctor to run another test.