How can anyone be this bad

How could someone make you feel so sick that you can't stand to be around them. There is a guy I work with and he just drives everyone crazy. No one wants to be around him and just about want to take him out. For three weeks now I have been dealing with him by myself so to speak since all the other staff took off on us for two weeks and on top of that I have to spend another two weeks with him. Well Friday night he had my head stressing so bad I could have taking him out myself. I know that he means well but I think he has ADA or some kinds of other ailment that takes over the brain. He really needs to be checked out to see if there is something truly wrong with him. I never seen someone who you tell over and over and he still just don't get it. I don't think he truly understands what it takes to do his job or any other job. How are we screening people these Days before hiring them. For two Days now I have cut him off I just can't even deal with him right now and wished he had stayed back. He has done a good job here this week so I wont take them from him. I know that he drives everyone crazy, but I can't even imagine if he drives his wife this crazy or how does she even stand it or deal with him. Maybe it is just me but I never had anyone stress me out like this before. I'm still pissed at the one these two weeks have turned out and I will tell you and anyone that this isn't funny being with him and for the person who actually set this up you will get yours in return one Day.