Squinters are anything that tastes so sour that it makes a person squint.
Typically, certain varieties of apples and first crop grapes, and other fruits, are so sour they will make a person squint.
Mary tried one of those grapes but decided not to buy any because they are squinters.
Ben made an apple pie using some squinters.
Those plums are so sour they are squinters.
Presinoia describes a Delusional Disorder, a mental health condition where any political aspirant who suddenly and genuinely believes he/she has a chance of getting elected POTUS (President of the United States); when in fact, those chances are the exact same as he/she becoming the next Pope, or Czar of Russia, or the Grand Vizier of BoogaBoogistan.
Think of any marginal or fringe candidate of any political party who "announces a committee" to explore the possibility of running for POTUS.
In 2011, there are dozens of such people, mostly Republicans, but other political parties as well, who are political aspirants for the 2012 POTUS election cycle.
Sam Smith announced he is running for President. He must be suffering with presinoia. His chances of getting elected are zero.