Thoughts on job interviews

• Recently I have had to interview a number of candidates for technical support positions at my work, and it has been rather an eye-opener. I'm no stranger to interviewing people, but never have I seen such a consistent range of inappropriate behaviours.
  Let's start with the most minor: dress. Now, I do not believe that dress code is at all appropriate for the average tech support position, but I like to see someone make an effort for the job interview itself. Preferably a jacket and tie. Failing that, at least a shirt. But, no. Quite a few of the people I've been seeing (for what is actually a fairly well paid position) just show up in jeans and t-shirt. Guy a couple of weeks ago came in the varient of an old sweatshirt, with t-shirt on top, a combo which irritates me even outside work. OK for beer and pizza, maybe, but not a job interview.
  Then there is the demeanour of the person. It is pleasant for everyone to keep it relatively informal and friendly. But it is a job interview after all, and I don't think much of people that laugh loudly, crack jokes, or lean back in their chairs and put their hands behind their heads as if to nod off.
  And show up on time for god sake.
  And the rambling on and on. There is virtue in keeping answers short and to the point.
  And when speaking of past jobs, there is really no point in letting me know that their previous manager had it in for them (for some unknown reason, or because they were a given religion, or whatever.) Maybe that is true, maybe it isn't, but bringing it up in an interview tends to be rather unimpressive.
  There is another one that I have seen, which isn't irritating, but rather a bit sad. I have a set lot of rather easy technical questions that I put to people in the interview. Those that don't have the necessary skillset, and can't answer most of my questions correctly, inevitably quickly assure me that they are both a very quick learner, and would be an asset to the company. Sorry man, maybe that it true, but I need someone with a certain base skillset.